Hi Allen, yes it does seem strange that SRM sell their alloy sump plate with only one size of socket cap.
However, I was looking at the part numbers of the studs and crossed referenced them with the list of threads for each nut/bolt on BSA's Triumph's etc. I have a copy of this list on my PC as the website which hosted it closed a while back, but I believe its available again and was mentioned on this site, but I cant find it.
Anyway the list mentions the following:-
- for bikes starting in 1970, the stud is part no 14-1401, the thread cross reference says its - UNC/UNF 1/4" 20/28 threads, 1" length
- for bikes up to the crossover year 1969, the stud is part no 31-0222 - BSW/BSF 1/4" 20/26 threads, 7/8" length
So the thread in the crankcase is either BSW (pre 1970) or UNC (1970 onward). I can imagine that trying to screw a UNC stud into BSW hole might be difficult and even though they are both 20 TPI the thread form is different.
The reason SRM supply socket caps may be that it makes the job easier when screwing into a BSW thread, otherwise vise grips may be needed to screw the stud in.
You learn something new everyday.
I haven’t looked in the 69 parts book for a while, and know most studs and threads are unf/UNC I’m quite surprised the sump cover is British thread and BSW at that. Also that probably does answer the SRM screw question, they always seem tight when threading into a set of cases so I prefer not to use them and stick with studs and use lock nuts