Contact Breaker Plate Pillar Screw

WEM said:

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.

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WEM said:

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!

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