12 Point / Double Hex size?

Discussion in 'Engineers' Talk' started by soabar, Jul 5, 2019.

  1. soabar

    soabar Member

    I'm trying to figure out what socket size I need for some 12 point bolts, they have 120° corners so I'm assuming double hex rather than triple / XZN & the heads, point to point are 7.07mm across. I've has a look at the regular online fastener spec pages, but I'm not coming up with anything.

    Dumb question, but are regular bi-hex sockets used with 12 point bolts or are they specific?

    If it's of any use this is on a hermetic motor which I think originated in Europe.

  2. KIAB

    KIAB Well-Known Member

    Post a photo.
  3. soabar

    soabar Member

    Not mine, it looks like this without the recess;

  4. KIAB

    KIAB Well-Known Member

    12 point socket?

    12 point socket dimensions
    Last edited: Jul 5, 2019
  5. sospan

    sospan Well-Known Member

    Do you need to keep the bolts as they are ? You may be able to remove them with a mole wrench and then replace them with a conventional bolt
  6. soabar

    soabar Member

    KIAB - Yes, it's 12 point but the corners are 120° rather than 90°(bi-hex, not tri-square).

    sospan - not enough access for grips unfortunately.
  7. Diyloser

    Diyloser Active Member

    Whats it off.?

    Need to work out in its metric or not first
  8. soabar

    soabar Member

    The bolts are in a hermetic motor / pump, pretty similar to a fridge motor & they hold the manifold / chamber caps down. I think it's of European manufacture (no markings) & the other internal fastners are metric. The two black bolt heads at the top of this image (one has the pipe turned round it) look roughly similar;

  9. Diyloser

    Diyloser Active Member

    Look to be either 8 or 10mm, a standard 12 point socket should be all thats needed.
  10. JustPhil

    JustPhil Active Member

    Yeah I’m used to 12 point bolts on automotive stuff that fits a normal 12 point socket. If it’s European assume metric. Standard 12 point socket set should fit?
  11. robertpstubbs

    robertpstubbs Active Member

    It’s similar to the bolts used on Land Rover brake callipers. You should be able to find a socket that will fit, but you may have go through metric, inch, and BSW/BSF to find the best fit.
  12. KIAB

    KIAB Well-Known Member

    12 point spline socket which is different to a 12 point socket.
  13. robertpstubbs

    robertpstubbs Active Member

    Multiply the point to point by 0.866.

    0.866 is 1.732 divided by 2.

    1.732 is the square root of 3.

    A Land Rover calliper bolt is 12mm in diameter. The point to point size is 15mm. 15mm x 0.866 = 13mm. A standard 13mm socket fits the bolt.

    7.07 x 0.866 = 6.12mm.

    Try a 4BA socket which is 6.3mm.
  14. robertpstubbs

    robertpstubbs Active Member

    Actually 1/4” isn’t much bigger at 6.35mm.

    On the other hand you may get a 6mm socket on.
    KIAB likes this.
  15. soabar

    soabar Member

    Thanks for the input folks.

    It looks like it isn't metric after all, 6mm bi-hex is too small, 7mm too loose (I don't have any bi-hex sockets, but realised a bit late in the game that i've got bi-hex ring spanners.....). After looking at a bunch more online dimensional tables it looks like it is 1/4 as robertpstubbs has suggested;

    7.07mm = 0.278" = 1/4 AF (across the corners).
  16. robertpstubbs

    robertpstubbs Active Member

    Other sizes to consider are 1/16BSW (Whitworth) which is 0.256” / 6.5mm, and 17/64” (0.266” / 6.76mm).

    Unfortunately the sockets in these small sizes are normally hex rather than bi-hex. Also they may not be currently made.

    Old British manufacturers like Britool made them. These old companies often gave their tools ref nos based on thou. Eg with Britool:
    DH248 = 4BA
    DB250 = 1/4”
    DH266 = 17/64”

    Under the Britool system the D means 1/4SD and A would mean 3/8SD. The H means hex and B means bi-hex. The 3 numbers are the size in thousandths of an inch.
  17. soabar

    soabar Member

    No access to anything but metric & squat available locally, so a 1/4" bi-hex ordered online & fits perfectly!


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