Bolt thread 6mm 14-15tpi

[tabbypurr]

We have a bolt as above on an office chair, probably from Staples. Anyone know what the official description of said bolt is?

NT

[Adrian]

6mm shank diameter? So M6. 1.75mm pitch would put 15 threads at 26mm, so M6 x 1.75

That'd be ridiculously coarse thread for a bolt that small, though.

[Fredxxx]

Something is wrong somewhere.

M6 x 1 coarse or M6 x 0.75 fine

25tpi would give M6 x 1

To have a thread pitch of 1.75mm it would have to be M12 x 1.75

I can't believe they would use a non standard bolt.

[tabbypurr]

no

It is. But... it is.

NT

[tabbypurr]

I've no idea why they have, but it's certainly not just a standard coarse M6.

NT

[GB]

I know nothing about bolt threads, but if this was for adjusting the chair's angle of lean or spring tension, you might need a bolt that moved a lot for not many turns?

Wouldn't it involve an awful lot of skilled work if you had to make your own tools - taps and so on - as well as presumably machining the bolts individually?

[Adrian]

OK... That's kind of fundamental to knowing what the description is...

[newshound]

So is it not so much a conventional bolt, going into a nut or a tapped thread in a metal component, but rather a self-tapping fastening to go into plastic?

[polygonum]

Assuming a) it did come from Staples; b) you need to replace the bolt, then ask at Staples! We did and got absolutely excellent service directly from the manufacturer. I think it was without charge. (From memory, our issue was casters.)

[tabbypurr]

no, it's a bolt holding the seat on. One fell out between annual checks. Any sane designer would not have used a supercoarse thread, but they did.

It did. Thank god for Mr Whitworth.

NT

[newshound]

Well as per my other post, are you sure that it isn't actually a self-tapping bolt? Perhaps going into plastic, or else a very soft alloy?

[tabbypurr]

It goes into a metal nut-like insert, like those pronged nuts.

I suppose I could ask Staples if they do spares, but I assume they won't, a nd I'm used to seeing £5 per screw prices for spares. Plus same again for p&p of course.

NT

[tabbypurr]

It wobbles in the thread until done up tight, so it can't be a self tapper. They've just chosen a weird thread for some reason. I'd have to rip the upholstery off to change the insert, so that isn't very practical.

Re asking staples, I want longer ones anyway, so it wouldn't get me far asking them.

NT

[Andy Burns]

Drill or prise the insert(s) out and replace insert and bolt with something standard?

[newshound]

Well the standard fix which I sometimes do for stripped threads, but which might work in this case, is to glue a suitable length of studding into the hole using araldite (or perhaps JB weld for an extra strong fixing), and then fix the removable part in place with a nut and washer. Epoxy normally bonds well to metal, especially if you degrease it carefully first. Applying a bit of heat also helps, once you have the knack.

[F Murtz]

A picture next to a rule would probably have saved many posts.

[Dave W]

It goes into a metal nut-like insert, like those pronged nuts.

I suppose I could ask Staples if they do spares, but I assume they won't, and I'm used to seeing ?5 per screw prices for spares. Plus same again for p&p of course.

NT

------------------------------------------------------ In May this year, the knob that holds the adjustable back into my office chair broke off. The metal bolt part was 5/16" UNC. I was able to buy one

2.5" long hex-headed bolt from Spalding Fasteners on ebay for ?1.64 including postage. I then melted its head into the plastic knob by heating the bolt with a blowlamp while holding it in pliers. Perhaps your bolt also has a UNC thread.

[Andy Burns]

If it was imperial, the closest size to a 6mm would be a 1/4" for which UNC would be 20tpi, not 14-15tpi.

[Alan Dawes]

Is it possible to pinch the prongs of the nut-like insert closer together and then use a standard M6 x 1 (metric course) bolt?

Alan

[tabbypurr]

NT