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Contact Breaker Plate Pillar Screw

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

  1. WEM

    WEM

    Joined:
    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.

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

    dynodave

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

    Bob beat me by 2 seconds:D
     
  4. WEM

    WEM

    Joined:
    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

    Joined:
    Nov 20, 2004
  6. 850commando

    850commando

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

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