The new oil switch I have ordered in looks like it has a tapered thread. The broken old oil switch I removed may well have had a parallel thread. It didn't leak when the engine was last running.
What thread should the oil switch have - parallel or tapered? Does it matter? (I suppose a tapered thread is required after previously fitting one)
As I recall BSA never fitted any taper thread fittings at the factory, but I have come across a couple of US imports where a taper thread has been forced in, and in one case this taper thread had cracked the area around the switch.
Oil pressure switches were produced with two types of thread, tapered or parallel, the latter had a copper compression washer for preventing oil leaks rather than relying on the tapered thread for sealing.
The female thread in the inner timing cover is always parallel threaded not tapered.