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Contact Breaker Plate Pillar Screw

Discussion in 'Norton Commando Motorcycles (Classic)' started by WEM, Apr 5, 2019.

  1. WEM


    Dec 8, 2017
    I'm wondering if there is a special tool required for the pillar screws that attach the contact breaker plate. A 5/16" wrench is too small and a 3/8" wrench is too big. An 8 mm wrench is too small and a 9 mm wrench is too big. I can use an adjustable wrench but I'm curious whether there's something that actually fits properly.
  2. Bob Z.

    Bob Z.

    Mar 30, 2012
    It is a 2BA wrench.
  3. dynodave


    May 28, 2003
    British bike
    British hardware
    British wrench
    2BA = .324"

    Bob beat me by 2 seconds:D
  4. WEM


    Dec 8, 2017
    Thanks. I just googled it and found this information...
    "They are unusual in that they were probably the most "scientific" design of screw, starting with 0BA at 6.0-mm diameter and 1.0-mm pitch and progressing in a geometric sequence where each larger number was 0.9 times the pitch of the last size. They then spoiled this by rounding to 2 significant figures in metric and then converting to inches and rounding to the thousandth of an inch. This anticipated worldwide metrication by about a century. The design was first proposed by the British Association in 1884[1][2] with a thread angle and depth based on the Swiss Thury thread,[3] it was adopted by the Association in 1903."
    Makes perfect sense!
  5. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Nov 20, 2004
  6. 850commando


    Nov 1, 2014
    and we crap on the germans for over-complicating a design...:eek:

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