Hitchcocks Forum

Hi. Can someone confirm the thread on the crankcase drain plug set in the side of my 1951 350cc bullet?
The diameter appears to be 9/16" but I'm not sure of the thread, whether it is whitworth, UNC or other.
Thanks

Appears to be 9/16 x 12 tpi Whitworth.

Well it will not be a Unified or Metric thread unless somebody has retapped the hole for some reason. It is most likely a BSCY cycle thread and at 9/16 diameter it could be 20 or 26 tpi. Tims suggestion appears logical but at 12 tpi you would only get 2 or 3 threads in the casting. Where are you located? Perhaps there is somebody close by who could check it for you. Have you thought to call our hosts as they know all things Enfield?

don't think a cycle thread would be in a casing

Thanks for your contributions.

It is a very coarse thread, only three and a half over the full length of bolt.

The plug is the same as the level/filler plug in the primary chaincase. I have tried my thread guage and it appears to be 12tpi but
not a very good fit.

The reason I ask is because there is another plug in the base of the crankcase which seals an oilway which has a bodged screw in it. The drain plug will screw in half way but I don't want to force it, I'd rather run a tap down it, if I can find the correct size.

It's probably Whit but I will see if our hosts have the definative answer.

Dave

All whithworth into aluminium and 26 tpi 60 degree for everything else.

Cheers, Simon.
Just ordered a 9/16 Whit tap.

Definitely 9/16 whitworth thread.
Received new drain plug from our friends and also have run a 9/16 whit tap down the thread.
Another bodge sorted!
Dave