Bren Tripod Rebuilding help request

A general question. What threading system was used on the Bren Tripods? S.A.E. or Withworth or BSW or ??
Area I'm working on are the leg pin threads. It seems that they are 14 tpi. Dia .625 inch or 5/8 inch. Which is not a normal SAE size, but they are available. Or does anyone have any other size for the leg pins?
Granted I could just replace the pins and collars by ordering them from brp. But I like to clean them up by chasing the treads with a tap or die as needed.
FYI it seems that a M12-1.50 tap fits the threaded hole on the front AA adjustable leg. Not sure if that is the perfect one but it sure cleans out the threads.
I've been rebuilding the leg pin areas. I'll take pics and post at a later time. Simple enough but you can have problems with the holding pins and the collars. Well have about 5 more setups to finish up.
THANKS for any help in advance.

Later 42rocker

Quote:

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Originally Posted by 42rocker

M12-1.50 tap

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I don't know if metric or imperial threads were used on Bren tripods but if the correct size thread, in this instance, is a 1/2" Whitworth thread form, BSW or BSF, putting a metric tap through the hole may/could damage the threads. Whitworth thread forms have a 55 degree angle of thread but metric thread forms normally have a 60 degree angle of thread. If a tap or a die is being used to clean up a thread it needs to be of the correct size, not what one thinks may be correct.

Well said, but what is correct? Your help please.

Later 42rocker

After spending a few hours finding and reviewing diagrams, I find that the specs always have BSF sizing.
Therefore I Thank all for reviewing my help request and can offer the above BSF statement.
Now off to try to figure out if I should if I should buy a BSF tap and die set or just replace everything if there is a problem.

So folks if working on a Bren Tripod I would say BSF taps and dies.

Later 42rocker

You should be able to get BSF taps and dies on eBayUK or from other UK based suppliers.

You probably don't need to go to the expense of buying a complete set of taps and dies and you could just buy the individual ones that you actually need for your project.

I always believed we Brits always used a good oldBritish thread until I tried to find the thread on the STEN barrel nut. Who would have thought ANS was the answer!

Regarding the tripod, are the threads obviously damaged? I’ve found them to be either extremely tight or slacker than a hookers ......handbag.

What threads are damaged? Well to start with only one area. Personally I like to chase the threads trying to clean them out of grease and such stuff. The major problem in the Bren Tripod is the pin hole that is drilled in the end for a couple to pins to be pressed in and the collar and handle going over them of course. As I'm buying surplus sometimes you have small pieces of metal thread or pin pieces or whatever that you might run into. I've been having fun with 18 sets of them. The collar and pin that goes in it at the end of the bolt, I have several that someone else before me really had messed up while taking apart. Looks like they used a long pipe wrench and just took the handles right off. Rip and tear. I've won the fight in 16 and will win the other two. I'm going to replace and throw away parts as it's cheaper to buy and replace things than to pay more for taps and dies and wait 30 days plus to have them shipping in from India.
As far as I can tell the major tap and die needed is the BSF 5/8-14. Measures .625 and thread pitch gauges show 14 tpi. It's used "I believe" for the front and rear legs threaded screws and handles. Only other area is on the mk1 AA front leg handle and screw setup.
If all goes well when I'm done I'll try to post a drawing with all of the thread sizes that I've found out and such. Need to head off to work.

Later 42rocker

If you only need to "clean up" a tapped hole you can make up a thread chaser to clean out the thread by using a bolt of the correct size and grinding 3 "nicks" in the end of the bolt to mimic the flutes of a tap. It won't cut a new thread but it will clean out a thread. The bolt being used to make the chaser obviously has to be the same thread as what you wish to clean out.

This tip is not something that I have thought up myself but was told to me years ago by a former Royal Engineer, sadly no longer with us, who was part of the BEF that evacuated from the beaches of Dunkirk. He return to France in the days following D-Day.

Thank you for the idea of making your own cleaning "tap". Problem on it is that it seems all of the threads on a Bren Tripod are BSF. Well walking out to my garage might produce 500 to 1,000 different bolts they are all in either SAE or Metric system. BSF threaded items are not common over here in the States. Of course might be in someone else's garage.
Well like I said I'll try to pop up a mk1 Tripod pic with the BSF thread sizes on it as I have found them.

Later 42rocker

Ordered a 3/16 to 3/4 inch BSF tap and die set to help out restoring some more Bren Tripods I just got in.

Such Fun.

Later 42rocker

Well, got the mini set of BSF tap and dies in. Working good on cleaning things up.
So far just using 2 sizes.

Later 42rocker