Which stud on a SIII transfer box

I think you will find the stud is 5/16" whitworth/BSF not UNC/UNF

Martin

I am pretty certain the thread in the casting is 5/16 Whitworth. JD

Even Land Rover are very unlikely to have mixed BS threads on one end with Unified on the other. Therefore if you have UNF at the outer end the other is most likely to be UNC. Similarly BSF outer end, BSW inner.

Get the stud that you intend to use and check it.

You don't actually need the special insertion tool to put in a Helicoil - although it is much easier if there are several to be done. For a one-off a piece of bar of the thread minor diameter, slotted across the end to take the tang will do. You do need to take care that the Helicoil doesn't get wound up like a spring outside the hole. This way you're only buying the tap and inserts.

Could you borrow a tool?

There is another insert design - Keensert - which uses standard taps (as opposed to the specials used with Helicoils). They don't do BSW, though. They can be less of a fiddle to install and the kits may be cheaper (no real knowledge, just a guess)

I actually checked the stud against a 5/16" whitworth plug tap and it's the same 18tpi, but so is UNC, only the thread form is different and that's subtle (55 instead of 60 degrees and slightly different crest and root) so I'll have to find those Whitworth thread gauges and see if I can tell the difference. Aren't standards a wonderful thing!.

Greg

Yes - trouble is there are too many of them. As I said, in that size, for practical purposes UNC and Whitworth are interchangeable - neither the stud nor the helicoil will have been made with small enough tolerances that they won't interchange, even if a little tight. JD

interchangeable.

And as I said (I don't know why I bother) the thread is Whitworth, if you don't believe me put your thread gauge on the other end to see if it's B.S.F or U.N.F and try a 1/2" or 1/4"Whit open ended spanner on the nut and see which one fits.

Martin

Yes I think it'll make little difference, the real problem will be getting the tap in without having to remove the whole seat box 8-(. Greg

The transfer case is quite thick on the top, can you use a longer stud to reach any good threads left in? If it is stripped all the way through then you might be able to tap it out to 3/8" Whit or UNC using a short tap under the seat box without drilling as 3/8" is only 3/4 of a millimetre either side bigger for the thread depth. A short socket head setscrew will miss the casing on the front holes (unless you want to keep it looking original make a two diameter stud). You can remove the rear power take off cover and bearing housing to catch any swarf. Save a lot of messing about.

HTH Martin

Yes you're quite right, the outer end is 22tpi so BSF, thanks for pointing me in the right direction. Greg