1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Annoying British Screw Size

Discussion in 'Tools and Materials' started by JohnD, 28 Aug 2020.

  1. JohnD

    JohnD

    Joined:
    15 Nov 2005
    Messages:
    66,172
    Thanks Received:
    3,587
    Location:
    Coastal
    Country:
    Cook Islands
    I am trying to match a pre-metric screw in an oldish English lock. Probably from the 1980's though it was designed in the 1960's or 1970's, and the factory probably used their existing tools.

    It is almost M4 (later versions of this same model lock have an M4) but an M4 binds and will not go beyond around half a turn, so the thread is obviously wrong although the size is about right.

    I thought it was UNC #6-32, which enters, and screws home tightly, so the thread must be about right, but is a very loose fit and wobbles (until it is screwed tight enough for the head to be tight)

    So what can it be?
     
  2. Sponsored Links
  3. big-all

    big-all

    Joined:
    12 Jul 2004
    Messages:
    18,412
    Thanks Received:
    1,420
    Location:
    Surrey
    Country:
    United Kingdom
    you have the thread pitch as well ??
    1/8 off an inch would off course be 3.175mm
     
  4. raykf

    raykf

    Joined:
    28 Feb 2010
    Messages:
    19
    Thanks Received:
    3
    Location:
    Norwich
    Country:
    United Kingdom
    4BA ?
     
  5. JohnD

    JohnD

    Joined:
    15 Nov 2005
    Messages:
    66,172
    Thanks Received:
    3,587
    Location:
    Coastal
    Country:
    Cook Islands
    The screw is only about 5mm long, so quite difficult for me to count TPI.

    I believe #6-32 is about 3.5mm major dia, so the size I need must be nearer 4mm, but in a non-metric size. #6-32 has 32TPI and threads easily into the parts. M4 just about fits, but will not go more than half a turn as the thread is wrong.

    I don't think I've got any 4BA, though I have some 2BA for a different purpose. I think of BA as an electrican's thread. 4BA is 3.6mm major, so I think would still be loose.

    Funnily enough the old screw is marked as Pozidriv, so it must be "transitional" screw they used before going over to metric.
     
  6. JohnD

    JohnD

    Joined:
    15 Nov 2005
    Messages:
    66,172
    Thanks Received:
    3,587
    Location:
    Coastal
    Country:
    Cook Islands

    Maybe it's 5/32" ?

    just under 4mm
     
  7. JohnD

    JohnD

    Joined:
    15 Nov 2005
    Messages:
    66,172
    Thanks Received:
    3,587
    Location:
    Coastal
    Country:
    Cook Islands
    I reckon it's probably Whitworth

    5/32" BSW
    32 TPI

    that would explain the #6-32 UNC screwing in at 32TPI
     
  8. big-all

    big-all

    Joined:
    12 Jul 2004
    Messages:
    18,412
    Thanks Received:
    1,420
    Location:
    Surrey
    Country:
    United Kingdom
    arnt the screws in electrical sockets or switches about 3mm ??
     
  9. JohnD

    JohnD

    Joined:
    15 Nov 2005
    Messages:
    66,172
    Thanks Received:
    3,587
    Location:
    Coastal
    Country:
    Cook Islands
    Modern electric socket and switch faceplate screws are M3.5

    but old (very old) UK switches and sockets had, I think, 2BA screws to hold the fronts on (and probably other sizes in other electrical equipment).





    5/32" BSW Csk Stainless machine screws are hard to find....
     
  10. Sponsored Links
  11. Harry Bloomfield

    Harry Bloomfield

    Joined:
    30 Dec 2018
    Messages:
    3,254
    Thanks Received:
    422
    Country:
    United Kingdom
    No, those were smaller than 2BA, maybe 4BA. 2BA were used in conduit boxes.
     
    • Thanks Thanks x 1
  12. JohnD

    JohnD

    Joined:
    15 Nov 2005
    Messages:
    66,172
    Thanks Received:
    3,587
    Location:
    Coastal
    Country:
    Cook Islands
    Ah yes, that's what I was thinking of.
     
  13. JohnD

    JohnD

    Joined:
    15 Nov 2005
    Messages:
    66,172
    Thanks Received:
    3,587
    Location:
    Coastal
    Country:
    Cook Islands
    just found that 5/32 BSW is size of Meccano screws.

    But no use to me, I need CSK stainless.
     
  14. bennymultifinish

    bennymultifinish

    Joined:
    21 Apr 2020
    Messages:
    2,004
    Thanks Received:
    300
    Country:
    United Kingdom
    3/16 whit normally in old locks.
     
    • Thanks Thanks x 1
  15. JohnD

    JohnD

    Joined:
    15 Nov 2005
    Messages:
    66,172
    Thanks Received:
    3,587
    Location:
    Coastal
    Country:
    Cook Islands
    ah, but that has a major diameter of 4.763mm, so my M4 screw should have dropped into it... but was a tight fit and would only go about half a turn before binding :(

    TPI of 3/16" is 24, but a UNC of 32TPI threaded in easily (but was loose)
     
    Last edited: 28 Aug 2020
  16. JohnD

    JohnD

    Joined:
    15 Nov 2005
    Messages:
    66,172
    Thanks Received:
    3,587
    Location:
    Coastal
    Country:
    Cook Islands
    well, I ordered some 3/16" BSW and some 5/32" BSW.

    The 3/16" arrived but are definitely too big and the thread is too coarse.

    Hoping the 5/32" will arrive and be the one.
    Didn't manage to locate CSK stainless yet.
     
  17. bennymultifinish

    bennymultifinish

    Joined:
    21 Apr 2020
    Messages:
    2,004
    Thanks Received:
    300
    Country:
    United Kingdom
    cant you retap the holes to suit a slightly larger thread.
     
Loading...

Share This Page