Tripod thread - confused!!

[Andrew*]

I thought I had the tripod thread question sussed, but things have just got all shaken up.

I have removed the head from my Horizon tripod. It attaches with an ordinary tripod screw. I then tried to screw it onto a 1/4" whitworth bolt that I bought a couple years ago, but it only goes on 3/4 of a turn and gets stuck.

I screwed a 1/4" whitworth nut onto the tripod legs and it goes on fine, just as it does onto said bolt. So clearly the threads on the tripod and on the bolt are very similar, if not the same, but still, the bolt will just not go into the hole on the tripod head!

I then tried out a bolt that usually goes in the top of skywatcher tube rings - a tripod thread as I understood - but even that won't go in the tripod head!

Strangely, the head goes on the tripod thread on the tube ring of my Topic refractor, and screws happily on the Horizon tripod.

What is going on?

Andrew

[davew]

Your right about the thread 1/4 20 BSW.

The head hasn't got a UNC has it ?

Strange.

Dave.

[Peter Drew]

1/4 Whitworth screws and 1/4 UNC screws have the same number of threads per inch, however, the Whit has a 55 degree included angle on the thread form and the UNC has 60 degrees. so, a Whit thread will fit a UNC but not vice versa unless the UNC "male" fit is undersize or the Whit "female" fit is oversize.

[Andrew*]

The confusion continues. I'm pretty positive that all the threads I'm dealing with are 1/4 BSW. The bolts I have work fine in another tripod head.

TBH, the threads do look a little worn on the one I'm trying to screw onto, but I don't know why it works on the tripod but not the bolt.

Shall I just force the bolt in and hope for the best?

[Bizibilder]

Don't force it! As stated above there is a mixture of thread "standards" used in telescopes and camera attachments (made worse if your gear is a few years old!). Just to confuse things further it is only the bolts that are supposed to go into "cameras" that are 1/4 W 20tpi. Any other thread is at the discretion of the manufacturer and may even be 6mm!! (or 6.5mm which is closer but less "standard").

Thread standards are a nightmare.