[planenut]

Originally Posted by COLVERT

Exactly, what you say is true.------That's why, in my previous post, I suggested to the OP to take along with him an adjacent bolt as a pattern. If you have that then you can exactly check the two bolts match for length, diameter and thread.---

Ah, there lies a problem, this is the only bolt of it's type on the engine. It is fitted into a threaded recess from the transmission into the sump using an Allen Key. Luckily there was no evidence of leakage due to it having been missing.

It may be a Torx fitting. I have found something on the Rimmers site but the dimensions are not shown, part number TRF000050, but it's not available.
Thank you all for comments.