UNC & BSW interchangeable?

[Peter Taylor]

Hi

Can I use a 3/8"-20 BSW bolt in 3/8"-20 UNC thread? I'm making an adapter plate for my theodolite tripod so I can mount a camera or spotting scope. The tripod screw is 5/8" UNC and I've managed to source the drill and taps for this end of the plate. But at the other end, the tripod head has a 3/8" UNC socket and I need a bolt to screw into it. Just one. There are only about 5 turns in the socket.

The only UNC bolts I can find on Ebay are from USA and the postage is ?27! So can I cheat and use a BSW bolt?

Cheers

[Dave Plowman (News)]

[Roger Mills]

Technically they're not interchangeable because the thread angles are slightly different - but to all intents and purposes they *are*, especially for relatively light loads.

[Peter Taylor]

Thanks Dave, I forgot to mention it needs to be brass. :)

[Peter Taylor]

Thanks Roger, that's what I'll do then. The bolt will only be finger tight.

I wondered if the threads would bind or be too loose. I didn't have any way of testing it, so thanks for the info.

Peter

[Martin Brown]

You might find them in various local metalwork dealers that cater for imported US cars.

Although brass might not be an option. If you say where you are then someone might be able to point to a helpful shack or Alladin's cave.

[Peter Taylor]

"Martin Brown" wrote

That's a good thought! I have a friend who drives a pink Cadillac (I think). I'll ask him.

I'm near HIgh Wycombe (Buckinghamshire).

[Adrian]

Orbital Fasteners in Rickmansworth or HMF in Amersham. I seem to remember there's a fastener place in Chesham, too, near the Lido.

If none of that lot can help, and none know anybody that can, then you're definitely going to be down to specialists on t'web.

[PeterC]

In that case you're near the cave and the pink Caddy would be enough to get you in! ;-)

[Dave Plowman (News)]

Trying to think what you'd use such a (relatively) large ordinary brass bolt for on any car. Special types for some electrics, possibly.

[Dave Liquorice]

Weren't exhaust down pipe to manifold bolts brass at some point?

[Roger Mills]

I think it may have been just the nuts which were brass - and they'd probably have been 5/16 rather than 3.8

[dennis]

[Peter Taylor]

Thanks Dennis, that's a very useful resource I hadn't found before.

Here's a pic of the tripod:

The tripod has a flat top plate with a hole about 80mm diameter in the centre, through which the brass fixing screw projects. The screw is free to move around in the hole to enable the theodolite to be positioned accurately over a point on the ground. This means I can't use the conversion bushes, and the only way I can think of to keep the screwsolidly in a fixed position is to use a brass bridge spanning across the hole, drilled and tapped

5/8" UNC for the screw, and this bit works fine. The problem is the bridge needs to be min. 10mm thick, otherwise the end of the screw projects above the surface, and that's too thick for any camera screws I've seen till now, which is why I was intending to use a bolt.

The screw in your link with 15mm thread length might be long enough, but it still leaves only 5mm thread above the bridge and I'm not sure that's going to be really secure, but I'm going to order some to try.

Discussing it with a friend yesterday he suggested reducing the thickness of the bridge locally for the screw using a spotface cutter, which means the

15mm screw will be OK. It would also let me use a circlip to retain the screw.

Getting there slowly! Thanks very much for your link.

Peter

[Dave Liquorice]

Oh thanks for that. Prices might be a bit steep. Doesn't have what I really want, 1/4" or 3/8" female in a sensible thickness plate no larger than about 3/4" that would bolt to a small plastic box.

[Martin Brown]

This lot will do custom engineering for a price (as will Telescope House).

They also have a lot of other useful and rare photographic goodies.

[Dave Plowman (News)]

Usually steel studs with brass nuts.

[Dave Plowman (News)]

Does it need to be brass? Is it for an underwater camera? ;-)

A decent engineering workshop should be able to turn one up for you out of brass. But it would cost.

[Mr Fuxit]

Peter, I have some 3" x 3/8" BSW Brass bolts, nuts and washers that you are welcome to. Also, I have a matching second-cut tap that I will lend you if you need it.

Please answer through the group, as I am having problems with e-mail. HTH!

[Mr Fuxit]

My e-mail problem is cured; please e-mail if I can help!