How do I use my coil crimpers?

Coil crimpers are the final step in the coil binding process — and the step most often done incorrectly, resulting in coil spines that unwind from the document, catch on pages, or look unprofessional at the ends. Crimping correctly takes less than 10 seconds per document but makes a significant difference in both the appearance and durability of the finished binding. This guide covers the correct crimping technique, common mistakes, and how to get consistent professional results every time.

For a complete overview of the coil binding process from punching through threading and finishing, see our comprehensive guide on how to bind a document using spiral coil binding.

What Is a Coil Crimper and What Does It Do?

A coil crimper is a hand tool — typically resembling a pair of flat-nosed pliers with a small channel or groove in the jaw faces — designed to flatten and bend the last loop or half-loop of a spiral coil binding at both ends. The crimping action serves two purposes: it prevents the spiral coil from unwinding backward through the document holes (which would cause the entire binding to come apart), and it creates a smooth, finished end to the coil rather than the raw sharp cut end that would otherwise protrude and catch on pages, hands, or bags.

Without crimping, a coil binding is technically complete but functionally incomplete. The cut ends of the coil have sharp wire tips that catch on everything they touch, and the coil can gradually back out through the holes over time as the document is used and the natural spring tension in the coil works against the threading direction. Proper crimping eliminates both problems in a few seconds. For guidance on the coil itself — selecting the right diameter and pitch — see our supplies guide at what coil binding supplies you should have.

The Two Parts of a Correct Crimp

Part 1 — Flattening

The jaws of the crimper flatten the last portion of the coil loop — compressing the circular coil cross-section into a flatter profile. This flattening serves two purposes: it increases the diameter of the coil at that point (making it harder for the loop to back through the last punched hole), and it stiffens the end of the coil so it doesn't spring back to its circular shape and work free of the document over time. Flattening should extend approximately 1/2 to 3/4 of the last loop — not just the very tip.

Part 2 — Bending toward the document

After flattening, the crimped end should be bent slightly toward the document edge rather than pointing straight out or away from the document. This bend ensures the crimped tip sits flush against the document's outer edge rather than sticking out as a snag point. The correct bend angle is approximately 45 to 60 degrees toward the document spine edge — enough to tuck the end against the document without being so severe that the coil looks deformed or the crimp breaks through the coil material.

How to Use Coil Crimpers — Step-by-Step

Step 1 — Complete the coil threading

Thread the coil fully through all the punched holes in the document. The coil should extend approximately 1/2 to 1 full loop beyond the last hole at both the top and bottom of the document. If the coil protrudes more than 1.5 loops beyond the last hole, trim the excess with coil cutters before crimping — over-long coil ends produce ungainly crimps that are harder to tuck cleanly. For threading guidance, see our step-by-step binding article at how to bind with spiral coil. For thick document coil binding considerations, see our guide on options for binding thick documents. For antimicrobial binders used to organize coil-bound document sets in shared environments, see our overview at antimicrobial binders.

Step 2 — Position the crimper on the top coil end

Open the crimper jaws and position them around the last 1/2 to 3/4 of the coil loop extending beyond the top hole. The jaws should be perpendicular to the coil axis — if the jaws are at an angle to the coil, the crimp will be off-center and the bend direction will be unpredictable. For most handheld crimpers, the groove in the jaw faces should align with the coil wire as you close the jaws.

Step 3 — Apply firm, even pressure

Squeeze the crimper handles firmly and evenly to flatten the coil end completely. Don't release partway — a half-squeezed crimp that's partially flattened and partially round provides less holding power than a fully committed crimp. Listen for the coil to stop compressing (typically a slight resistance change) to know the crimp is complete.

Step 4 — Bend the crimped end toward the document

While still holding the crimped end in the jaws, tilt the crimper toward the document spine edge at approximately 45 degrees. This bends the flattened tip toward the document rather than away. Release the jaws — the crimped tip should now point toward and slightly into the document edge rather than outward. For coil sleeves that complement professional crimping at the spine, see our guide at how to use coil binding sleeves.

Step 5 — Repeat for the bottom coil end

Repeat the same process for the bottom coil end. Consistency between the top and bottom crimps produces the most professional finished appearance. Check both ends visually — both should be flattened by the same amount, both should point toward the document at roughly the same angle.

Step 6 — Test the finished binding

Try to pull the coil backward through the document from both ends with moderate hand force. A correctly crimped coil should resist firmly — if you can feel the crimp starting to pull back through the last hole, the crimp wasn't flattened enough or the coil end was too short for adequate holding. For guidance on coil selection for your specific application, see our machine buying guide at what to look for when buying a coil binding machine.

Quick Reference — Crimping Checklist

Troubleshooting

Coil is pulling out through the end holes after crimping

The crimp wasn't flattened enough, or the coil end was too short. The flattened portion must be wide enough that it can't pass back through the punched hole. Trim the coil to leave at least 1 full loop beyond the last hole, and apply a more aggressive crimp that flattens at least 3/4 of that last loop.

Crimped end is sticking out and catching on things

The crimp was applied but not bent toward the document. Apply light pressure with the crimper and bend the tip toward the document edge. If the tip has already been sharply bent away, re-crimping to reverse the direction may crack the coil material — in that case, trim back and crimp fresh material.

Coil end snapped off during crimping

The coil wire was too brittle, possibly due to cold conditions making the PVC harder and less flexible, or the crimp was applied with excessive force at a sharp angle. In cold environments, warm the coil slightly before crimping. Apply even pressure directly perpendicular to the coil axis rather than at an angle.

Crimps look uneven — one end looks good, the other doesn't

Inconsistent technique between the two ends. Focus on applying the same amount of jaw coverage (1/2 to 3/4 of the last loop) and the same bend angle at both ends. Consider practicing the crimp motion on scrap coil until the technique is consistent before crimping finished documents.

Electric coil inserter is available — do I still need to crimp manually?

Yes — electric coil inserters thread the coil but don't crimp the ends. Manual crimping with a hand crimper is still required after electric insertion. The crimping step is always a manual final operation regardless of whether threading was manual or electric.

Frequently Asked Questions

Do I need a special crimper for each coil diameter?
Most handheld coil crimpers work across the full range of standard coil diameters (6mm to 50mm) because the jaws are sized to accommodate various coil widths. Some commercial crimpers have specific jaw sizes optimized for narrow ranges. For most office and small shop applications, a single universal crimper handles all standard coil diameters. For coil supply selection, see our guide at what coil binding supplies you should have.

What happens if I skip the crimping step?
Without crimping, the cut coil ends have sharp, raw wire tips that catch on pages, hands, and bags. More importantly, the coil can gradually back out through the holes as the document is opened and closed repeatedly, eventually working completely free and causing the binding to fall apart. Crimping takes less than 10 seconds per document — it's always worth doing.

Can I use regular pliers instead of a dedicated crimper?
In a pinch, yes — flat-nosed pliers can flatten and bend a coil end. The result is typically less consistent and less clean than with a dedicated crimper because the jaw geometry isn't optimized for coil wire. For occasional emergency use, pliers work. For regular production, a dedicated crimper is worth the minimal investment.

How much coil should extend beyond the last hole before crimping?
Approximately 1/2 to 1.5 loops. Less than 1/2 loop doesn't give enough material for a reliable crimp. More than 2 loops is excess that should be trimmed with coil cutters before crimping — an over-long end produces an ungainly crimp that's harder to tuck cleanly against the document edge.

Is there an electric or automatic crimper available?
Some commercial coil binding machines include integrated automatic crimping as part of the binding cycle. These are production-level machines that thread and crimp in a single automated operation. For standard desktop coil binding, manual crimpers are the standard tool. For guidance on production coil binding equipment, see our machine guide at what to look for when buying a coil binding machine.