The name crimping pliers is used for two different tools. What they have in common: both make something smaller by squeezing it.
1. Crimping pliers for pipes and ducts
These cut a series of slits in the end of an aluminium or sheet metal pipe and then swage that end in, so it takes on a slightly smaller diameter. That lets two pipes of the same diameter slide into one another: the crimped end fits just inside the other pipe.
Uses: thin sheet metal ventilation ducts, the extract duct of a cooker hood, and making fittings to size. Points to watch:
- Wear gloves. A slit pipe edge is sharp.
- In ventilation, airtightness matters. A crimped joint is not automatically sealed — tape the joint and secure it with self-drilling screws or pop rivets.
- Always crimp in the direction of flow. In extract ducts carrying grease or moisture, the inner pipe must sit inside the outer one in the direction of flow, so no lip is formed for dirt to catch on.
2. Crimping pliers for connectors
These press a metal sleeve, cable lug or connector permanently around a conductor. That is how an RJ45 plug goes on a network cable, or a ferrule, ring terminal or spade terminal onto an electrical conductor.
For a sound crimp:
- Use the right die. Every conductor size and connector type has its own profile in the tool. The wrong die gives a joint that looks fine and does not hold.
- Use a ratcheting tool. It only releases once the full crimping force has been reached — which is exactly the difference between a reliable and an unreliable joint.
- Do not solder afterwards. A crimp is a gas-tight cold weld; running solder over it makes the transition brittle.
- Pull test it. Give the conductor a firm tug after crimping. If it pulls out, the crimp was not right.
Related terms
- Cable lug
- Ferrule
- Ventilation duct
- Pop rivet
- Tools
- Electrical installation
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