Aviation Snips

Aviation snips, also called compound snips or tin snips, are hand shears with a compound-lever mechanism that multiplies hand force, allowing clean cuts in sheet metal. They take their name from their early use in aircraft sheet metal work and are now standard tools for metal roofers, gutter installers, sheet metal and HVAC workers.

Colour code

A widely used convention colours the handles by cutting direction:

• Red: left-cutting snips, which cut curves counter-clockwise and make straight cuts where the waste falls to the left.
• Green: right-cutting snips, for clockwise curves.
• Yellow: straight-cutting snips, which can also cut wide curves.

The colour refers to the cut direction, not to whether the user is left- or right-handed. Some manufacturers use other colours for specialty tools such as seamers and crimpers.

Variants

• Offset snips keep the hand above the work so long cuts can be made without the cut metal fouling the hand.
• Long-cut snips for straighter, longer cuts.
• Bulldog or heavy snips for thicker material.
• Power shears and nibblers, electric tools used for long cuts in panels, which avoid the heat and burred edges caused by abrasive discs.

Capacity

Tool reviews indicate typical aviation snips cut up to about 18 gauge cold-rolled steel or 22 gauge stainless steel, though capacity varies by model. Aluminium, copper and zinc cut more easily than steel of the same thickness.

Roofing practice

Roofers use snips to notch panels at eaves and ridges, trim flashing, cut around penetrations and finish trims. Metal roofing manufacturers generally discourage abrasive cut-off wheels on coated steel because hot filings embed in the finish and rust, and because heat can damage coatings at the cut edge. Snips and shears produce cleaner, cooler cuts. After cutting, filings should be swept off the roof promptly.

Safety

Cut sheet metal edges are very sharp. Gloves rated for cut resistance and eye protection are standard, and cut-offs should be collected rather than left on the roof.