I looked up my cone/freehub dustcap measurements for 7 speed hyperglide (with the external uniglide threads on the freehub)

All drive side dustcaps have an od of 29.5

6400 tricolor has a 17mm cone and dustcap has a 21 id, using a rubber seal fitted to a slot in the cone

1055 and M452 (and similar) uses a 17 cone with mechanical seal (2 cut metal washers) and a 18mm id dustcap

I’m not sure how the RM-30 compares, but if it does, maybe try the ISO thread, some people may be looking for the uniglide cones and dustcaps -

the ones I mentioned (seem to me) to be much more plentiful than the uniglide parts (the short uniglide cone and dustcap was critical in getting a tricolor to fit 120 spacing, using a 6speed uniglide body)

Good luck

Joe