25D4 'side-entry' cap, which positions the HT leads well clear of the RHD steering column and UJ, unlike top-entry caps. Cut ends of the leads push into the holes:

... and are secured with screws:

25D4 'top-entry' cap, these silicone-cored leads have crimped metal terminals that push into connector sockets inside the cap:

Nothing inside the cap except the five connections, the centre one being a spring-loaded 'carbon' or graphite rod:

In the image above you can see how the 'boot' on No.4 plug lead has been gouged by nut on the steering column UJ (circled) if the leads are allowed to take the most direct route to the plugs, more info on that here.

45D4 'top-entry' cap, with connector sockets for push-in leads with connector plugs:

Again nothing inside except the five connections:

For RHD cars where the steering column UJ can rub the leads DDB194 side-entry 45D cap for push-fit leads suitable for clip mounting (as well as screw as on the Mini) may also be an answer: (Powerspark)

Failures: A nearly new 45D4 cap with the carbon contact missing, and fragments of spring floating around inside, which has worn and burnt the (also nearly new) rotor. Subsequently the contact was found lying on the points plate. Photos: David Bolton

The rotor:

Years later (March 24) another example of a 45D4 from Graeme Stoten - business end on the left, other end on the right showing where the stub for the spring has snapped off:

The spring and the remains of the stub left in the cap. Judging by any signs of arcing on the plug lead contacts this cap looks brand new:

The rotor, negligible to no signs of burning unlike David Bolton's after only a few miles:

Another failure, new and 'Lucas' branded, this time the retaining springs had punched through the cap and shorted out the HT Photo: Richard Thompson

Signs the rotor has been rubbing on the cap, which may or may not be the cause of the misfire that led to this investigation (Nat Bristol). Make sure the rotor is pushed fully down on the shaft.