Contact Breaker Plate Pillar Screw

[WEM]

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.

 

[Bob Z.]

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.

It is a 2BA wrench.

 

[dynodave]

British bike
British hardware
British wrench
2BA = .324"

Bob beat me by 2 seconds

 

[WEM]

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!

 

[L.A.B.]

http://www.sat.dundee.ac.uk/~psc/spanner_jaw.html#Jaw_Size_Table

 

[850commando]

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!

and we crap on the germans for over-complicating a design...