[Hallicrafters] Bristol Spline drive set screws

[Charlie]

I have been asked several questions about the Bristol drive set screws so 
here's a compilation of them.

1)The Bristol drive set screws have generally become obsolete with the 
introduction of the Torx drive.  They are still used in some commercial 
applications, as they are superior in their torque ratings.
2)The Bristol drive resembles a splined drive shaft with square sided 
flutes, whereas the Torx drive has rounded flutes which will remind you of 
an end view of an umbrella.
3)There are incidences where an Allen hex drive key will fit into a Bristol 
socket, but it is not a true mating fit.   If the torque required is VERY 
low, the Allen wrench MAY be made to work, but the risk of damage to the 
splines is not worth it.
4)The actual set screw threads used are identical to all other set screws, 
so either a slotted or Allen drive set screw can be substituted for the 
Bristol drive with no worry.
5)I'm not sure what determined whether the various Bristol sizes used six or 
four splines.  You would think that the smaller sizes would all drop to 
four, but this is not the case.
6)Possible sources for the Bristol wrenches are: Jensen Tools, Techni-Tool, 
McMaster-Carr, MSC Hardware, Grainger and probably any commercial 
hardware/tool supplier.
7)The Xcelite part numbers for the four I use are:  99-67, 99-66, 99-64 & 
99-63.  These will fit any of Xcelite's various size handles.  The complete 
set of inserts and a drive handle is packaged under their part number 
99-PS-60 which typically sells for around $40.00
8)Sets of "L" wrenches are also available at the Bristol website
9)I have a source for Bristol set screws that I bought in order to supply 
the correct ones with the new production Dakaware knobs I purchased a few 
years ago.  As I am contemplating another large quantity knob buy, I find 
that unfortunately, the Bristol set screws have gone up considerably in 
price.

73' Charlie k3ICH