What kind of thread could this be?

[Chris]

Trying to make up a puller for a steering wheel (Land Rover) so it's imperial (it really is in this instance!) Can anyone tell me which imperial thread is frequently confused for 6mm metric? To be a bit clearer, I can't use my thread gauges in this instance because they're a bit too wide to probe the hole in question. But a 6mm threaded rod *will* go in nicely like it's a perfect fit - up to a point! After several turns, however, it binds up. So... what imperial bolt size & thread type would this most likely be? Something very close to 6mm metric but 25 TPI. AF? UNF? UNC? Any ideas?

[The Nomad]

1/4" 10TPI would be my guess (so UNC?)

Avpx

[newshound]

Not 10 tpi surely? 1/4 Whitworth and UNC is 20 tpi, 1/4 BSF is 26.

M6 coarse is 1 mm pitch (so 25.4 tpi). So pretty close to BSF.

[F Murtz]

May be 1/4" whitworth (20 TPI I think)

[Chris]

Perhaps I didn't make myself clear enough earlier. Whatever this thread is, it's very, very close to 25TPI. Like *VERY* close if not spot-on. This is because the 6mm rod that almost fitted is *very* close to 25TPI. Cheers.

[Cursitor Doom]

He must mean UN*F*C, I would guess. ;->

[Chris Hogg]

Don't forget 0BA: 6mm OD, 25.38 TPI, pitch 1mm

[Dave Plowman (News)]

What age is the Land Rover? Before metric, most UK car threads were unified. UNC for threads into ally - but for steel and nuts and bolts generally UNF.

6mm would be closest to 1/4" UNF/C. The spanner which fits that is 7/16th AF. The next size up in UNF/C is 5/16th. About 8mm.

Generally, in terms of thread pitch, UNC is closer to metric than UNF.

[Adrian]

Do you need a puller?

Leave the centre nut on a turn or two, and give the wheel a really good wiggle and a thump from behind and a wiggle and a thump from behind. It'll let go soon enough. When it does, you will WANT that centre nut still on - else you'll get a steering wheel in the face...

[Chris]

Tried it already. The problem is the more modern LR steering wheels are very rubbery affairs and lack the rigidity necessary for such an approach to succeed. Anyway it's probably just as well it didn't work as I'd left off the centre nut! :-D

[Harry Bloomfield]

Chris a écrit :

1/4" Whitworth. I have a box of mixed 6mm and 1/4 Whitworth roofing bolts and nuts, they are quite hard to distinguish apart, without testing them.

[Chris]

Brilliant! Turns out to be 1/4" Whit fine at 26tpi to be precise; many thanks indeed.

[newshound]

Then it is 1/4 BSF.

[newshound]

Sorry, or 0 BA (havn't checked but do not doubt Chris's figures).

[newshound]

Never heard of Whitworth fine; British Standard Fine, on the other hand, is 26 tpi.

[Chris]

That's what I meant: BSF (AKA Whitworth fine) there's a Whitworth course as well, it seems. So many thread forms!!!

[newshound]

It's the same thread form as Whitworth (1841), but was actually defined much later (1908).

[Cursitor Doom]

The rest of the world must marvel at us. They use simple V forms of 60' and we have all these fancy variations of 55' with a radius of one size or another on the crests and roots of threads and nuts. They must wonder how the f*ck we ever won both World Wars pissing around with intricacies like that.

[F Murtz]

Well BSF.

[Chris]

Oh, a typo flame! How frightfully droll.