How to crimp a bootlace ferrule
Updated: 21 October 2026
You have a ratchet ferrule tool, a reel of sleeves, and stranded flex on the bench. The circuit is isolated, or you are practising on an offcut. This page is how to crimp a bootlace ferrule in one full cycle, and how to recognise a bad crimp or a stuck ratchet. The kits sit on the [crimping pliers set comparison](/hub/pliers/crimping-pliers-set). A qualifying purchase can earn us a commission at no extra cost to you. Strip to the tube, crimp only the metal, and do not open the tool until the cycle finishes.
You have a ratchet ferrule tool, a reel of sleeves, and stranded flex on the bench. The circuit is isolated, or you are practising on an offcut.
You have a ratchet ferrule tool, a reel of sleeves, and stranded flex on the bench. The circuit is isolated, or you are practising on an offcut. This page is how to crimp a bootlace ferrule in one full cycle, and how to recognise a bad crimp or a stuck ratchet. The kits sit on the crimping pliers set comparison. A qualifying purchase can earn us a commission at no extra cost to you. Strip to the tube, crimp only the metal, and do not open the tool until the cycle finishes.
Our top picks
| Badge | Product | Ferrule range | Jaw | Ratchet | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Preciva Preciva ferrule crimper set, 1,200 sleeves | 0.25–10 mm² | Square, self-adjusting | Forced lock | 9.4 | about £22.99 | View offer |
| Alternative |  Preciva Preciva ferrule kit with twin sleeves | 0.25–10 mm² | Self-adjusting | Pressure adjustable | 9.4 | about £23.99 | View offer |
| Best value |  Hibisaws Hibisaws ferrule kit, 1,250 sleeves | 0.25–10 mm² | Square, self-adjusting | Pressure wheel | 9.0 | about £19.99 | View offer |
On this page
Set the strip and the ferrule size
Read the millimetre squared on the ferrule collar, not the plastic colour. Those codes are not the red, blue and yellow bands on insulated rings. If the flex is 1.5 mm², take a 1.5 mm² sleeve.
Strip so the copper matches the metal tube, not the collar. RS’s sequence is choose the size, strip, twist splayed strands lightly, then slide the collar on until the copper sits flush with the tube. Copper that sticks out folds under the screw. Copper that stops short leaves the tube half empty. Do not tin the strands.
Regulation 526.9 is why the ferrule is crimped before the screw. If you are unsure a ferrule belongs, read bootlace ferrules and BS 7671 first. Two conductors need a twin sleeve marked for that pair.
One squeeze until the ratchet lets go
Open the ratchet fully and offer the metal tube to the die, not the coloured collar. The collar should sit just outside the jaws. A red, blue and yellow nest is the wrong shape. Change tool rather than squeezing harder.
Close the handles in one stroke until the ratchet releases on its own. Klein’s 3005CR instructions, for a different tool, say the same: once a cycle starts, the handles do not release until it completes. A half-closed die slides off on the first tug.
A sound crimp is compact, the copper is still flush, and the collar has not split. Tug the sleeve. If it moves, cut it off and start with a new ferrule. The screw comes after that tug.
If the tool sticks or the sleeve pulls off
A ratchet that will not open halfway is doing what it was built to do. Find the release latch near the pivot, open it, and throw the partial ferrule away. Reusing a half-closed tube hides a weak joint.
If the sleeve pulls off after a full cycle, check the die, the printed size and the strip length before you squeeze harder. A three-colour nest on a bootlace is a different failure, and the ferrule crimper or insulated terminal crimper page is that split. A 1.0 mm² sleeve on 1.5 mm² flex will not hold. If the handle cover has slipped, refit it before you hide the joint.
Where this sequence stops
This sequence is for an isolated circuit or an offcut on the bench. A consumer unit, meter tails, or a protective conductor you cannot identify is not a practice bench. Hire an electrician. Plastic handles on a £20 kit are not live-working insulation.
Aluminium conductors, BS 7609-size power cable from 10 mm², and any joint you cannot isolate sit in the same stop. The crimping pliers set buying guide is where you choose a ferrule kit rather than a ring kit. An RJ45 pass-through tool trims a plug as it closes. That is a different sequence.
If the tug test fails twice on a new ferrule and a matching die, stop. The sleeve in the box may be the limit, not your stroke. A pretty crimp that slides off is worse than leaving the work unfinished.
Common questions
How long do I strip the wire?
Strip so the exposed copper fills the metal tube and sits flush with the end. The coloured collar is not part of that length. Copper that sticks out will fold under the screw. Copper that stops short leaves the tube half empty. Match the printed mm² first, then cut the insulation to the tube.
Do I tin the strands first?
No. Slide the ferrule onto bare, lightly twisted strands and crimp the metal. Solder under a later screw can creep. The IET point is that the ferrule is crimped before the screw, not soldered and then squeezed.
Where does the collar sit relative to the jaws?
The die should close on the metal tube. The coloured collar sits just outside the jaws so the plastic is not crushed into the copper. If the whole sleeve disappears into a red, blue or yellow nest, you are using the wrong tool.
What if the handles lock halfway?
Find the release latch near the pivot, open the tool, and throw the partial ferrule away. Do not force the handles apart through the ratchet. Start again with a new sleeve. A half-cycle is not a finished crimp.
How do I know the crimp worked?
The barrel looks compact, the copper is still flush, the collar has not split, and a firm tug does not slide the sleeve. Then, and only then, the ferrule meets the screw. The screw does not finish the crimp.
Can I crimp the same ferrule twice?
No. Cut it off and start again. A second bite on a distorted tube hides a weak joint. Recut the flex to clean copper and take a new sleeve.
What if the sleeve still pulls off?
Check the die family, the printed mm² and the strip length before you squeeze harder. A three-colour nest on a bootlace, or a 1.0 mm² sleeve on 1.5 mm² flex, will fail the tug. If those three match and the sleeve still slides, discard that brand of terminal.
Does this sequence work for an RJ45 plug?
No. A pass-through RJ45 tool trims pairs as it closes an 8P8C plug. Pair order, jacket length and the blade are a different job. This page is a bootlace ferrule on stranded flex.
Related pages
Sources
Public UK sources from the research digest, last checked on 19 October 2026. Shelf prices and star lines are the amazon.co.uk figures in the display file.
- IET Wiring Matters: Mythbuster 5, terminal blocks and ferrules (retrieved 19 October 2026)
- IET EngX: Ferrule crimps (retrieved 19 October 2026)
- IET EngX: Crimping of flexible cord conductors (retrieved 19 October 2026)
- BSI: BS 7609:1992+A2:2009, uninsulated power connectors (retrieved 19 October 2026)
- HSE: Electricity at Work Regulations guidance, HSR25 (retrieved 19 October 2026)
- RS: Bootlace ferrules (retrieved 19 October 2026)
- RS: Knipex 97 53 04 crimp tool (retrieved 19 October 2026)
- Klauke GB: Insulated solderless terminals (retrieved 19 October 2026)