Crimping a ferrule onto a stranded wire takes about 30 seconds once you have the right tools and sizing. The process has three stages: cut and strip the wire cleanly, slide the ferrule on, and compress it with a crimping tool positioned just in front of the plastic collar. Get those details right and you’ll have a solid, gas-tight connection every time.
What Ferrules Do and When You Need One
A wire-end ferrule (sometimes called a bootlace ferrule) is a small metal tube with a plastic insulating collar. You crimp it onto the stripped end of a stranded wire so the individual strands are compressed into a single, solid tip. That tip then slides cleanly into screw-type terminal blocks, push-in connectors, and similar terminations without any loose strands splaying out or getting damaged under the screw.
Ferrules are designed for stranded conductors. You don’t need one on solid wire, which already has the rigid shape that terminal connectors expect. The ferrule essentially converts a flexible, multi-strand wire into something that behaves like a solid conductor inside the terminal. This is especially useful for fine-stranded flexible wire classes, where individual strands are thin enough that a screw clamp can cut through them. For smaller stranded wires in the 16 to 20 AWG range, ferrules are particularly recommended because the fine strands are fragile and prone to damage during termination.
Choosing the Right Ferrule Size
Ferrules are sized to match specific wire cross-sections, and the plastic collar is color-coded to help you identify them quickly. The catch is that color codes vary between standards. A black ferrule indicates a 1.5mm² conductor under the DIN and French systems, but it marks a 6.0mm² conductor in the German Weidmüller system. Some standards also repeat colors at larger sizes. In the DIN system, red appears for 1.0mm², 10.0mm², and 35.0mm² conductors.
The safest approach is to check the size printed on the ferrule packaging rather than relying on color alone. Match the ferrule’s rated cross-section to your wire’s actual cross-section. A ferrule that’s too large won’t compress tightly enough around the strands, creating a weak connection. One that’s too small won’t fit over all the strands, and forcing it risks cutting or excluding individual wires.
Twin ferrules are also available for inserting two wires into a single terminal. These have a wider barrel designed to hold both conductors side by side.
Tools You’ll Need
You need three things: a wire cutter, a wire stripper, and a ferrule crimping tool. Regular pliers or generic crimpers won’t produce the right crimp profile and can damage the ferrule or leave a loose connection.
Dedicated ferrule crimpers have a ratchet mechanism that prevents the jaws from opening until they’ve fully compressed. This guarantees consistent pressure on every crimp. Most ferrule crimpers create either a square or trapezoidal crimp profile, both of which distribute force evenly around the metal tube. The tool typically has multiple die positions sized for different ferrule ranges, so you select the slot that matches your ferrule before crimping.
Self-adjusting ferrule crimpers automatically detect the ferrule size and apply the correct compression. These cost more but eliminate the step of manually selecting the right die position, which reduces the chance of using the wrong setting.
Step-by-Step Crimping Process
Cut the Wire
Start with a clean, straight cut across the conductor. Use sharp wire cutters and cut in a single motion. The goal is a flat end where all strands terminate at the same point. Avoid pulling, twisting, or crushing the wire during the cut. A ragged or angled cut means some strands won’t reach the full depth of the ferrule barrel.
Strip the Insulation
Remove enough insulation so the bare wire fills the metal barrel of the ferrule without extending significantly past it. The ferrule packaging or the ferrule itself will indicate the correct strip length, which corresponds to the barrel length. Use a wire stripper set to the correct gauge so you cut through the insulation cleanly without nicking the copper strands underneath. Damaged strands weaken the connection and defeat the purpose of using a ferrule.
After stripping, check that no insulation remains on the exposed section. Any residual insulation trapped inside the ferrule barrel will prevent proper metal-to-metal contact.
Insert the Wire
Slide the ferrule onto the stripped end of the wire. Push it on until the wire’s insulation butts up against the plastic collar of the ferrule and the bare strands reach the end of the metal barrel. You should be able to see the copper strands at the tip if you look straight on. If the strands are recessed deep inside or if they’re poking out well beyond the barrel, recheck your strip length.
Hold the wire and ferrule together to keep them from shifting before you crimp. Some people lightly twist the strands before insertion to keep them together, but avoid over-twisting, which can create a stiff bundle that doesn’t compress evenly.
Position the Crimper
Place the ferrule into the correct die position on your crimping tool. The crimp should land on the metal barrel of the ferrule, slightly in front of the plastic collar. Crimping on the collar itself won’t compress the metal tube properly. Crimping too far toward the tip may leave the rear portion of the barrel loose.
Crimp
Squeeze the handles fully. If your tool has a ratchet, it will prevent the jaws from releasing until the crimp cycle is complete. Don’t try to force the ratchet open early. Once it clicks open on its own, the crimp is done.
For ferrules with longer barrels (often used on larger wire sizes), you may need to crimp in multiple stages. Start at the end farthest from the collar and work your way toward the insertion end, placing each successive crimp adjacent to the previous one. This ensures the full length of the barrel is compressed evenly.
Checking Your Work
A good crimp has a few visible characteristics. The metal barrel should show a uniform, symmetrical impression from the crimping die, whether that’s a square, trapezoid, or hexagonal shape. The barrel shouldn’t be cracked, split, or deformed unevenly. The plastic collar should still be intact and sitting flush against the wire insulation, with no bare copper visible between the insulation and the collar.
Give the ferrule a firm tug. It should not slide off or rotate on the wire. If it moves at all, the crimp was too loose, likely from using the wrong die size or the wrong ferrule for that wire gauge. Cut the ferrule off and start fresh with a new one. Ferrules are single-use. Re-crimping a ferrule that’s already been compressed won’t produce a reliable connection because the metal has already deformed.
Finally, check that the crimped end fits smoothly into your terminal or connector. The ferrule tip should slide in without excessive force. If it won’t fit, confirm you’ve matched the ferrule size to what the terminal is rated for.
Working With Different Wire Types
Ferrules are commercially available with ratings for a wide range of stranding classes, from standard stranded wire all the way to highly flexible classes used in machinery and drag chains. When you’re working with fine-stranded flexible wire and need to terminate it in a connector rated only for solid or coarse-stranded wire, the ferrule bridges that gap. The crimped ferrule effectively gives you a solid-wire-rated end that’s accepted by the terminal’s listing.
For wire sizes 8 AWG and larger, ferrules convert the conductor to behave like a standard Class B or C stranded wire for termination purposes. For 10 AWG and smaller, the ferrule makes the wire behave like a solid conductor. In both cases, the terminal’s existing ratings for solid or standard stranded wire cover the connection once the ferrule is properly applied.