How To Cut Metal Duct – Safely & Precisely For DIY HVAC Projects
To safely and precisely cut metal duct, you’ll primarily use aviation snips (left, right, and straight-cut types) or tin snips for straight lines, along with a utility knife for insulation. Always wear heavy-duty gloves and eye protection to prevent injury from sharp edges and metal shavings.
Measure and mark your cuts accurately with a marker or scribe, then use the appropriate snips, making relief cuts for curves, and deburr all edges afterward for a clean, safe finish.
Embarking on a home improvement project involving ductwork can feel daunting. You might be staring at a shiny piece of metal, wondering, “How am I supposed to cut this without mangling it or, worse, myself?” It’s a common challenge for DIY builders and hobbyists alike.
Cutting metal duct effectively requires the right tools, proper technique, and a healthy respect for safety. Without these, you could end up with jagged edges, inefficient airflow, or even a trip to the emergency room.
But don’t worry! This comprehensive guide will transform that apprehension into confidence. We promise to walk you through every step, from selecting the correct tools to mastering precision cuts and finishing touches. You’ll learn the essential techniques, discover expert tips, and understand the best practices for how to cut metal duct safely and efficiently, ensuring your HVAC system performs optimally.
By the end of this article, you’ll be ready to tackle your ductwork project with skill and ease, making clean cuts and achieving professional results. Let’s dive in!
Understanding Metal Ductwork and Why Precision Matters
Before you even think about making a cut, it’s helpful to understand a bit about the metal ductwork you’ll be working with. Most residential and light commercial HVAC systems use either galvanized steel or aluminum ducting. Galvanized steel is steel coated with a layer of zinc, which prevents rust and corrosion. It’s durable and common. Aluminum ductwork is lighter and easier to manipulate but can be more prone to bending if not handled carefully.
Regardless of the material, precision is paramount when you’re learning how to cut metal duct. Sloppy cuts can lead to several problems.
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Air Leaks: Uneven edges make it difficult to create a tight, sealed connection between duct sections. Air leaks reduce the efficiency of your heating and cooling system, costing you money.
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Poor Airflow: Jagged edges or distorted ductwork can create turbulence, impeding smooth airflow and diminishing your system’s performance.
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Difficult Installation: Pieces that don’t fit together properly add frustration and extra time to your project.
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Safety Hazards: Rough, sharp edges are a major safety concern, both during installation and for anyone who might need to access the ductwork later.
By taking the time to learn the right techniques for how to cut metal duct, you’re investing in a more efficient, safer, and ultimately more successful project.
Essential Tools for How to Cut Metal Duct Like a Pro
Having the right tools makes all the difference when you’re working with sheet metal. Forget trying to hack at it with a utility knife – you need specialized equipment for clean, safe cuts. Here’s a rundown of what you’ll need, along with some how to cut metal duct tips for tool selection.
Hand Snips: Your Primary Cutting Companions
Hand snips are the workhorses for cutting metal duct. There are a few key types, each designed for specific cuts.
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Aviation Snips: These are your go-to tools. They come in three main varieties, color-coded for easy identification:
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Red-Handled (Left-Cut): Designed for cutting curves to the left. The blades are offset to the right.
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Green-Handled (Right-Cut): Ideal for cutting curves to the right. The blades are offset to the left.
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Yellow-Handled (Straight-Cut): Best for straight cuts and wide curves. They have straight blades.
You’ll want a set of all three for maximum versatility. They operate like heavy-duty scissors, making them easy for beginners to master.
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Tin Snips (Straight-Cut): These are larger, heavier-duty snips, primarily used for long, straight cuts in thicker gauge metal. While aviation snips are more agile, tin snips offer more leverage for robust tasks.
Marking and Measuring Tools
Accurate measurements are the foundation of good cuts.
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Measuring Tape: A standard retractable tape measure is essential. Make sure it’s sturdy.
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Permanent Marker or Scribe: A fine-tipped permanent marker or a metal scribe will help you make clear, visible lines on the ductwork.
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Straightedge or Square: A metal ruler, carpenter’s square, or combination square ensures your lines are perfectly straight and square.
Finishing and Assembly Tools
After cutting, you’ll need to refine the edges and prepare for assembly.
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Deburring Tool or File: Metal edges can be razor-sharp after cutting. A deburring tool or a metal file is crucial for smoothing these edges, significantly improving safety and fit.
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Sheet Metal Crimpers: These tools create a crimp on one end of a round duct section, allowing it to slide snugly into another section. They are indispensable for joining round ductwork.
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Utility Knife: If your ductwork has insulation, a sharp utility knife is perfect for cutting through it neatly.
Safety Gear (Non-Negotiable!)
This isn’t optional. Metal duct edges are incredibly sharp.
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Heavy-Duty Work Gloves: Leather or cut-resistant gloves are a must to protect your hands from sharp metal edges.
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Safety Glasses or Goggles: Metal shavings can fly, especially when cutting. Protect your eyes.
While some professionals might use power tools like nibblers or shears, for a beginner, focusing on quality hand snips is the safest and most practical approach to learn how to cut metal duct.
Prioritizing Safety: Your Guide to How to Cut Metal Duct Responsibly
Working with sheet metal can be dangerous if you don’t take proper precautions. Sharp edges, flying debris, and improper tool handling are all potential hazards. Embracing a “safety-first” mindset is the most important how to cut metal duct best practice.
Always Wear Personal Protective Equipment (PPE)
This is non-negotiable. Don’t even think about making a cut without it.
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Gloves: Wear heavy-duty, cut-resistant gloves. Standard fabric gloves won’t offer enough protection against sharp metal edges and burrs.
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Eye Protection: Safety glasses or goggles are essential. Small metal slivers can become airborne during cutting, posing a serious risk to your eyes.
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Long Sleeves: Consider wearing long-sleeved shirts to protect your arms from accidental scrapes and cuts.
Maintain a Safe Work Area
A tidy and well-prepared workspace significantly reduces risks.
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Stable Surface: Work on a clean, stable surface. A workbench with a vise or clamps can help secure the ductwork, preventing it from shifting unexpectedly.
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Clearance: Ensure you have plenty of room to maneuver the duct and your tools without bumping into obstacles.
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Good Lighting: Adequate lighting helps you see your cut lines clearly, reducing the chance of errors and accidents.
Proper Tool Handling and Usage
Knowing how to use your tools correctly is key to both safety and effective cutting.
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Sharp Tools: Use sharp snips. Dull blades require more force, increasing the risk of slips and awkward movements. Refer to our how to cut metal duct care guide later for maintenance tips.
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Correct Snips: Always use the appropriate snips for the job (left, right, or straight cut). Forcing the wrong snips can lead to poor cuts and hand strain.
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Keep Fingers Clear: Be mindful of where your non-cutting hand is positioned. Keep it well away from the cutting path of the snips.
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Manage Scrap: Immediately collect and dispose of cut-off metal pieces. They often have very sharp edges and can be tripping hazards.
Post-Cutting Safety
Safety doesn’t end when the cut is made.
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Deburr Edges: As mentioned, deburring is crucial. Smooth out all sharp edges with a file or deburring tool before handling the cut duct further.
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Store Tools Safely: Clean and store your tools properly after use. Don’t leave sharp tools lying around.
By following these safety guidelines, you’ll protect yourself and ensure your project proceeds smoothly and without incident.
Step-by-Step Guide: How to Cut Metal Duct for Various Shapes
Now that you’re geared up and safety-conscious, let’s get down to the practical steps of how to cut metal duct. We’ll cover marking, straight cuts, curved cuts, and round duct techniques.
Preparing Your Workpiece and Marking Your Cuts
Accuracy starts before the first snip.
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Clean the Duct: Wipe down the metal surface to remove any dust, grease, or debris that might obscure your markings.
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Measure Accurately: Use your tape measure to get precise dimensions. Double-check your measurements to avoid costly mistakes.
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Mark Clearly: Use a permanent marker or a scribe to draw your cut lines. For straight lines, use a straightedge or square to ensure they are perfectly straight and perpendicular. For curves, you might use a compass or a flexible ruler.
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Secure the Duct: If possible, clamp the ductwork to your workbench. This prevents movement and allows for more stable, accurate cuts.
Cutting Straight Lines with Aviation Snips
Straight cuts are fundamental to most ductwork projects.
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Choose the Right Snips: For long, straight cuts, yellow-handled straight-cut aviation snips are ideal. For very long cuts in heavier gauge metal, tin snips might be more comfortable.
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Start the Cut: Position the snips at the edge of the metal, aligning the blades with your marked line.
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Make Continuous Cuts: Squeeze the snips firmly but smoothly. Don’t close the blades completely with each squeeze. Instead, make partial cuts, opening the blades just enough to advance along the line without disengaging the metal. This helps prevent metal distortion.
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Keep Blades Open: Try to keep the cutting blades as open as possible during the cut, especially on the waste side. This reduces the risk of bending or deforming the good piece of duct.
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Avoid Over-Cutting: Stop just short of your end mark if you’re making a series of cuts that meet at a corner. You can trim precisely later.
Tackling Curved Cuts and Notches
Curved cuts require specific snips and techniques.
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Select Appropriate Snips: Use red-handled (left-cut) snips for curves turning left, and green-handled (right-cut) snips for curves turning right. The offset blades help keep your hands clear of the metal.
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Make Relief Cuts: For tight curves or intricate notches, make small, perpendicular relief cuts into the waste material leading up to your main cut line. These cuts allow the metal to flex and separate more easily, preventing buckling and making the curve smoother.
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Small Bites: Take smaller “bites” with your snips when cutting curves. This gives you more control and helps maintain the curve’s integrity.
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Work from the Edge: Always start your curve from an edge if possible, rather than trying to start in the middle of a sheet.
Cutting Round Duct Sections
Round duct often needs to be shortened or have notches for connections.
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Mark the Circumference: Wrap a tape measure around the duct or use a flexible rule to mark your cut line evenly around the entire circumference. A piece of masking tape can also serve as a straight edge for marking.
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Start the Cut: Make an initial cut from the edge of the duct up to your marked line, using straight-cut snips.
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Spiral Cut Technique: Once you reach your line, continue cutting around the duct in a spiral fashion. Angle the snips slightly to maintain the circular path. This helps prevent the metal from buckling.
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Finish the Cut: Complete the spiral until you meet your starting point. You may need to make a final, short straight cut to fully separate the piece.
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Crimping (if joining): If you’re joining two sections of round duct, one end will need to be crimped. Use sheet metal crimpers to create evenly spaced indentations around the circumference. This reduces the diameter slightly, allowing it to slide into another duct section.
Finishing the Edges: Deburring and Smoothing
This critical step often gets overlooked, but it’s vital for safety and proper fit.
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Identify Burrs: Run your gloved hand gently along the cut edge to feel for any sharp points or burrs.
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Use a Deburring Tool: A dedicated deburring tool is quick and effective for removing sharp edges from sheet metal. Simply run the blade along the cut edge, applying light pressure.
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Alternatively, Use a File: A metal file (a flat bastard file works well) can also be used. Hold the file at a slight angle and push it along the edge, always filing away from your body. Repeat on both sides of the cut until the edge feels smooth to your gloved touch.
These detailed steps will guide you in achieving clean, professional results every time you cut metal duct.
Common Problems When Cutting Metal Duct and How to Avoid Them
Even with the right tools and techniques, you might encounter a few hiccups. Knowing common problems with how to cut metal duct and how to troubleshoot them will save you time and frustration.
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Distorted or Wavy Edges: This is a frequent issue, especially with thinner gauge metal. It happens when you squeeze the snips too hard or try to take too large a bite.
Solution: Make shorter, more frequent cuts. Don’t close the snips all the way with each squeeze. Keep the blades as open as possible on the waste side to allow the metal to flow through without buckling. Use sharp snips. -
Uneven or Jagged Cuts: This usually stems from rushing or not following your marked line precisely.
Solution: Slow down. Take your time to align the snips with your marked line before each squeeze. Use a clear, visible mark and a straightedge for straight cuts. If a cut goes slightly off, don’t try to correct it abruptly; ease back onto the line. -
Excessive Burrs and Razor-Sharp Edges: While some burrs are inevitable, excessive ones indicate either dull tools or improper cutting technique.
Solution: Always use sharp snips. Make sure you’re cutting cleanly, not tearing the metal. Most importantly, dedicate time to deburring every single cut edge with a proper deburring tool or file. -
Dented or Damaged Ductwork: This can happen from dropping the duct, clamping it too tightly, or resting heavy objects on it.
Solution: Handle ductwork carefully. When clamping, use protective pads (like wood scraps) between the clamp jaws and the metal. Store duct sections properly to prevent accidental damage. -
Hand Fatigue: Repetitive squeezing can tire your hands, especially with many cuts.
Solution: Take breaks. Ensure your snips are comfortable and well-maintained. If you have a very large project, consider if a power shear or nibbler might be a better (though more expensive and advanced) option, but always prioritize safety training for such tools.
By being aware of these common pitfalls and applying these how to cut metal duct tips, you can anticipate and avoid most problems, leading to a smoother and more successful project.
Sustainable & Eco-Friendly Practices for Metal Duct Projects
As builders and DIYers, we have a responsibility to consider the environmental impact of our projects. Incorporating sustainable how to cut metal duct practices not only benefits the planet but can also lead to more efficient and cost-effective work.
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Minimize Waste Through Accurate Planning: The best way to be eco-friendly is to reduce waste. Carefully plan your duct layout and measurements before making any cuts. Precise planning means fewer miscuts and less scrap metal.
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Optimize Material Usage: When cutting multiple pieces from a larger sheet or length of duct, try to “nest” your cuts to maximize material usage and minimize offcuts. Think of it like a jigsaw puzzle.
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Recycle Scrap Metal: Metal ductwork (galvanized steel or aluminum) is highly recyclable. Don’t throw small scraps into the regular trash. Collect all metal offcuts and take them to a local metal recycling facility. Many scrapyards will even pay you for clean scrap metal.
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Choose Durable, Long-Lasting Materials: Opt for high-quality duct materials that are built to last. A well-installed, durable duct system will require fewer repairs and replacements over its lifetime, reducing resource consumption.
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Proper Disposal of Other Materials: If you’re removing old ductwork that contains insulation, ensure the insulation is disposed of according to local regulations. Some older insulation types may contain hazardous materials.
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Maintain Tools for Longevity: Properly caring for your cutting tools (as discussed in the next section) extends their lifespan, reducing the need for frequent replacements and the resources required to manufacture new tools.
Embracing these eco-friendly how to cut metal duct principles helps you build smarter and greener.
Maintaining Your Tools: A How to Cut Metal Duct Care Guide
Your metal cutting tools are an investment. Proper care not only extends their lifespan but also ensures they perform safely and effectively for every project. This how to cut metal duct care guide will help you keep your snips in top condition.
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Clean After Each Use: Metal dust and debris can accumulate on your snips, especially in the pivot points. Use a stiff brush or an air compressor to remove any metal shavings. A damp cloth can wipe down the handles and blades, but ensure they are thoroughly dried afterward to prevent rust.
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Lubricate Pivot Points: The pivot joint on your snips is crucial for smooth operation. Apply a drop or two of light machine oil (like 3-in-1 oil or WD-40) to the pivot point periodically. Open and close the snips several times to work the oil in, then wipe off any excess.
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Sharpening (When Necessary): While aviation snips are designed for durability, their blades can dull over time, especially with heavy use or if used on inappropriate materials. Sharpening snips can be tricky due to their unique blade angle. For most DIYers, it’s often more practical to replace severely dull snips, but professional sharpening services are available. Avoid trying to sharpen them with a standard file, as this can damage the blade geometry.
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Inspect for Damage: Before and after each use, quickly inspect your snips for any signs of damage like bent blades, loose pivots, or cracked handles. Damaged tools can be unsafe and perform poorly. Replace them if necessary.
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Proper Storage: Store your snips in a dry place to prevent rust. Many snips come with a locking mechanism to keep the blades closed, which is safer and helps protect the cutting edges. Hang them on a pegboard or store them in a toolbox where they won’t get dinged or dulled by other tools.
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Use for Intended Purpose Only: Resist the urge to use your metal snips for cutting wire, cardboard, or other materials they weren’t designed for. This can quickly dull or damage the blades, compromising their ability to cut metal effectively.
By following these simple maintenance steps, your essential metal cutting tools will remain reliable companions for many projects to come.
Frequently Asked Questions About Cutting Metal Duct
Here are some common questions aspiring carpenters and DIYers have when learning how to cut metal duct.
Can I use an angle grinder to cut ductwork?
While an angle grinder can cut metal duct, it’s generally not recommended for beginners or for most standard ductwork. Angle grinders produce a lot of sparks, heat, and metal dust, requiring extensive safety gear and ventilation. They also create a wider, rougher cut that’s harder to clean up and deburr, and they can easily distort thin sheet metal. For precision and safety in DIY HVAC, hand snips are almost always the superior choice.
What’s the difference between tin snips and aviation snips?
Tin snips (also called “straight snips”) are larger, heavier, and designed for long, straight cuts in thicker sheet metal, offering more leverage. Aviation snips are smaller, lighter, and spring-loaded, making them easier to use for prolonged periods. They come in left, right, and straight-cut versions, specifically designed for making accurate straight or curved cuts in thinner gauge ductwork with minimal distortion. For most HVAC work, aviation snips are preferred due to their versatility and precision.
How do I prevent metal distortion when cutting?
To prevent metal distortion, ensure your snips are sharp and clean. Make continuous, smooth cuts without fully closing the blades on each squeeze. Keep the blades open as much as possible, especially on the waste side, to allow the metal to pass through freely. Avoid twisting the snips or forcing them through the material. Using the correct type of snips for the cut (e.g., straight-cut for straight lines) also helps.
What if my cut is slightly too short or too long?
If a cut is slightly too long, you can often carefully trim off the excess with your snips, taking very small “bites” for precision. If it’s too short, it’s more problematic. For small gaps, high-quality HVAC foil tape or mastic sealant might bridge the difference. However, if the cut is significantly off, it’s usually best to recut a new piece of duct. Trying to force an ill-fitting piece can lead to leaks and poor airflow.
Do I need to seal the cut edges?
You don’t typically “seal” the cut edges themselves with tape or sealant. The purpose of sealing is to create airtight connections between duct sections. Once you’ve made your cut, deburr the edges to make them safe and smooth. When you join two duct sections, that’s when you’ll use foil tape, mastic sealant, or both, around the seam to ensure an airtight connection, preventing air leaks and maximizing efficiency.
You’ve now got a solid foundation for how to cut metal duct with confidence and skill! From selecting the right snips to ensuring a safe workspace and perfecting your cutting technique, you’re equipped with the knowledge to tackle your next HVAC project.
Remember, practice makes perfect. Start with small, manageable cuts, always prioritize safety, and don’t rush the process. Taking your time to measure accurately, make clean cuts, and deburr properly will lead to professional-looking results and a more efficient home system.
Keep those hands protected, your eyes covered, and your cuts precise. You’ve got this!
Stay safe and stay comfortable!
