[R-390] Bristol Screws

[JRFKE5RI at aol.com]

Here is some background information.
 
Bristol Wrench Co. - Bristol Spline Wrenches
Developed by  Bristol, the multiple spline drive system is recognized by 
design engineers as  the superior method of transmitting torque because nearly 
100% of wrenching  force is applied at right angles to the load bearing spline 
surfaces of the  socket. Other drive systems dissipate a significant amount of 
force into radial  thrust, tending to expand the socket rather than tighten the 
screw. The  substantial and effective wrench engagement inherent in the 
Bristol design  addresses the problems caused by other fastening systems such as 
cam-out, socket  reaming and "rounding" of wrenches.

Decades ago, Bristol engineers invented the Bristol Spline  Drive System for 
use in electromechanical instruments. They required screws and  wrenches that 
could stand up to industrial environments, vibrations, and  frequent removal 
and resetting. Bristol wrenches have been in continuous  production in the 
United States since their original introduction.
 
Source: Bristol Wrench Company  _http://www.bristolwrench.com/spline.pdf_ 
(http://www.bristolwrench.com/spline.pdf) 
 
Bye the way, if you try to use a standard Allen (hex) wrench,  your screwed.  
No pun intended.
 
John Felton
KE5RI