Page 1 of 2 12 LastLast
Results 1 to 15 of 17

Thread: BSA rear guard screw size? Superstar, Meteor etc

  1. #1
    Join Date
    Dec 2003
    Location
    Cambridge UK
    Posts
    5,822

    BSA rear guard screw size? Superstar, Meteor etc

    Can anyone confirm the thread size of the rear trigger guard screw for a Superstar / Meteor and other models? I am carrying out a little cosmetic work on a Superstar and the screw is a bit 'challenged cosmetically' although does work. I have tried various screws from my collection but failed to find a replacement. Searching around on this forum and the internet in general leads me to the conclusion it could well be UNF 8-36.
    I know I could buy a new one but that irks me a bit although to be fair, a search for unf 8-36 screws shows they are not very cheap anyway.

    I am told you can re-tap to 2BA but I see no need to do that. It might be more fun to get a 8-36 die and cut a new thread on a slightly oversize screw.

    Interestingly the front stock screws can be replaced with 4mm although I doubt that is the original size.

    All help appreciated.
    Cheers, Phil

  2. #2
    Join Date
    Jun 2014
    Location
    Chester
    Posts
    5,348
    Two bee eh all round.

  3. #3
    Join Date
    Apr 2019
    Location
    Gillingham dorset
    Posts
    80
    I tried googling this a while back and just bought (last week) of John knibbs. Think it was a fiver posted. Like you I tried dozens but I'm not technically minded so just bought that incase I screw the thread up

  4. #4
    Join Date
    Dec 2003
    Location
    Cambridge UK
    Posts
    5,822
    Quote Originally Posted by piggy589 View Post
    Two bee eh all round.
    Sorry but they are not. I tried a 2BA bolt in the rear guard just to see and it is not the right size. I found a thread somewhere that informed me that the manufacturer's thread could be retapped to 2 BA quite easily though. Maybe that is what you have come across. And the front stock screws are certainly not 2BA. 4mm fits but I doubt if that thread form is the original spec.
    Cheers, Phil

  5. #5
    Join Date
    Jun 2012
    Location
    Oslo, Norway
    Posts
    1,111
    M5 in my Supersports and Superstar. Thats the rear trigger guard screw, the fronts are M4.

  6. #6
    Join Date
    Dec 2003
    Location
    Cambridge UK
    Posts
    5,822
    This is getting more puzzling. Thank you evert. I tried M% but it was too big ... pity as I have a lot of them.

    I am wondering if the best solution is to strip the action and re-tap the thread.... and put a nice screw in place.
    Cheers, Phil

    At the same time ... if someone has an electronic version of the Owner's Manual, I would be very pleased to have a copy.
    Cheers again.
    Last edited by Phil Russell; 29-10-2020 at 07:29 PM.

  7. #7
    Join Date
    Jun 2012
    Location
    Oslo, Norway
    Posts
    1,111
    Quote Originally Posted by Phil Russell View Post
    This is getting more puzzling. Thank you evert. I tried M% but it was too big ... pity as I have a lot of them.

    I am wondering if the best solution is to strip the action and re-tap the thread.... and put a nice screw in place.
    Cheers, Phil
    So, after making this duboius assumption based on memory and a bunch of mixed up supersport parts, I realized that my contribution would just add more confusion. So I went and actually measured some screws on some guns:

    Late Supersport (presumably Birmingham made):
    Rear: M5X0,8
    Front: M4x0,7

    Early Mk2 Supersport and Superstar:
    Rear: measures in at about 4,6mm, and the thread pitch is VERY close to 0,7, and does not match up with any of my TPI gauges.
    Front: M4x0,7

    I measured a mk3 Meteor too:
    Rear: the same as the early Supersport and Superstar
    Front: not measured today, but earlier confirmed to be a 2BA (I actually made some screws that I threaded with a 2BA die for a meteor a while back.)

  8. #8
    Join Date
    Jun 2014
    Location
    Chester
    Posts
    5,348
    I must admit I've not had to source screws for later guns,up to mk6 meteor, 2 and 4ba used.

  9. #9
    Join Date
    Jan 2006
    Location
    Rossendale, Lancashire
    Posts
    1,096
    I can confirm that my Superstar, Supersport, Goldstar and even mk1 Lightning all have a 2BA x 1.5 rear guard screw. Front stock screws are all M4. Its not uncommon to see different fasteners mixed and matched, Webley did exactly the same.

    Cheers
    Greg

  10. #10
    Join Date
    Dec 2003
    Location
    Cambridge UK
    Posts
    5,822
    Well, thank you all for taking such trouble. I appreciate it. I wonder which thread the Knibbs part is.
    I am warming to the idea of retapping the thread now....
    Cheers, Phil

  11. #11
    Join Date
    Jun 2012
    Location
    Oslo, Norway
    Posts
    1,111
    Quote Originally Posted by Phil Russell View Post
    Well, thank you all for taking such trouble. I appreciate it. I wonder which thread the Knibbs part is.
    I am warming to the idea of retapping the thread now....
    Cheers, Phil
    Or you could get a more recent supersport/lightning rear block, that is threaded M5. Then you can change back if you want to get the gun original again.

  12. #12
    Join Date
    Dec 2003
    Location
    Cambridge UK
    Posts
    5,822
    Quote Originally Posted by evert View Post
    Or you could get a more recent supersport/lightning rear block, that is threaded M5. Then you can change back if you want to get the gun original again.
    Good point. But then again, the gun has seen a bit of attention from previous owner(s) so I do not think it needs to be in absolute original condition ... that would be a tad difficult to arrange.

    Cheers, Phil

  13. #13
    Join Date
    Jun 2012
    Location
    Oslo, Norway
    Posts
    1,111
    Measuring the screws and relating to the BA thread system got me confused, so I had to learn more about it.

    Its a British standard, so I expected the pitch to be imperial - but none of my imperial thread gauges matched the pitch of the early Supersport/Superstar rear screw. (clearly not a 30TPI, almost a 32TPI). The closest thread gauge I found is a 0.8 mm pitch - on a British thread system???

    Time for some googling!

    This page cleared up my confusion:
    https://journeymans-workshop.uk/baandme.php

    So, the table lists the 2BA as .185" diameter x 31.4" TPI!!! That does not really sound logical..

    But the text goes on to explain:
    "British Association threads were a metric thread system devised for small screws. Originally included even smaller sizes intended for use in watchmaking but these have been superceded by specialist horological thread series. Not metric like you might expect, but with diameters determined by a factor proportional to a power of the logarithm to the base 10 of the thread pitch in millimetres. Hence the rather strange mix of metric and imperial in the above table."

    Aha! Dividing 25.4mm (1") by 31.4 TPI gets you 0.809, so the close to 0.8mm pitch starts to make sense.
    The 4.6mm I measured with worn calipers is close to the listed .185", which translates to 4.7mm.

    Its a confusing (when compared to more recent thread standards) system, but the 2BA really is close to a M4.7x0.8 thread.

    Which is good for re-tapping to a M5x0.8 thread!
    Last edited by evert; 31-10-2020 at 07:51 AM.

  14. #14
    Join Date
    Dec 2003
    Location
    Cambridge UK
    Posts
    5,822
    Having stripped the relevant block out, I find a 2BA screw fits. Why a 2BA would not fit with the block assembled on the rifle in the first place I do not know. if this thread is really 2BA then it could explain the untidy appearance of the guard screw fitted. Maybe this screw was forced into a 2BA thread???
    Whatever ... onwards.
    I continued my look at the rifle by stripping it. Not too bad really but the spring guide was a pretty loose fit in the spring and the large circular end broken off. New guide is being made. Small O ring breech washer was somewhat damaged BS 010 seems to fit OK in the recess but I do not have the larger O ring. I think it is OK though. Mainspring seems fine... must measure it, as it the piston seal. I will also add a piston sleeve.
    So next ... trigger reassembly. Why do I expect coffee to be in demand?

    At least it is raining here so I would not be outside anyway.
    Cheers, Phil

  15. #15
    Join Date
    Jun 2012
    Location
    Oslo, Norway
    Posts
    1,111
    Quote Originally Posted by Phil Russell View Post
    Having stripped the relevant block out, I find a 2BA screw fits. Why a 2BA would not fit with the block assembled on the rifle in the first place I do not know.
    Some Supersports/Lightnings I have worked on have had alignment problems with the holes in the rear block and the holes in the cylinder.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •