18mm Spiral Binding Coils

The pitch of the coil and the punched document must match exactly. Most 18mm plastic coils for standard document binding use a 4:1 pitch, meaning the punch creates four holes per inch along the binding edge. A coil made for that pattern will not feed correctly through a document punched for another pitch. Before ordering, confirm the pitch stated for the coil, the punch pattern produced by the machine, and the number of holes along a sample sheet. This matters when supplies are being reordered for an older machine or when several binding systems are used in the same work area. Pitch is separate from diameter: 18mm describes the coil size, while 4:1 describes the spacing of the loops. Both details must be correct for reliable insertion and smooth sheet turning.

Not every machine is suitable. The machine must create the same pitch as the coil, normally 4:1 for this type of plastic spiral, and it must be able to punch the paper size being used. Its stated binding capacity should also accommodate the finished stack, even when punching is completed in smaller batches. Some machines only punch holes, while others include an electric roller that helps insert the coil. A manual setup can still handle an 18mm coil, but thicker documents take more care to align and feed evenly. When selecting among coil binding machines, consider punch pattern, punching capacity, document width, and whether regular production volume justifies powered insertion. Matching these factors prevents wasted supplies and reduces stress around the holes.

For a document bound along the 11 inch edge, a 12 inch coil is commonly used because it provides enough length to pass through the entire punched edge before trimming. The extra material at both ends is removed after insertion, leaving enough coil to form secure finished ends. Binding along a different edge changes the required length, so measure the punched side rather than relying only on the paper description. Oversized covers, index tabs, documents bound along a different edge, and custom sheets may also affect the best length. The coil should extend beyond both ends during insertion, but it should not remain excessively long after finishing. Ordering by diameter alone can lead to the wrong result, since diameter controls document thickness while coil length controls the span of the punched edge.

After the coil has been inserted, each end must be trimmed and bent inward so the spiral cannot unwind from the document during handling. A plain cut leaves an open end that can work its way back through the first or last punched hole. Proper crimping forms a small hooked finish that keeps the coil in place while still allowing the document to open flat and turn through a full rotation. The cutting jaw and crimping action must be oriented correctly at each end, since the direction changes from the top to the bottom. Purpose built coil crimpers give a cleaner and more consistent finish than ordinary scissors or pliers. Testing the crimp on one document before completing a large run helps confirm the tool position and final appearance.