[R-390] Weird looking set screws

[Fred Moore]

Aha!  I'm looking for six to ten of the 4-40 x 1/2 inch Bristol socket head
cap screws for the BFO and BW shaft clamps.  One square nut (if available)
would be helpful as well.  If not, I'm sure there would be Allen head screws
at my local hardware store. 

But What didn't work for the ham I got his from was a mix of slotted and
Phillips screws -- the heads wore out quickly.  

-Fred

------ Original Message ------
Received: Tue, 16 Jun 2026 03:32:34 AM GMT
From: robert meadows via R-390 <r-390 at mailman.qth.net>
To: R390A <r-390 at mailman.qth.net>, Tisha Hayes <tisha.hayes at gmail.com>
Subject: Re: [R-390] Weird looking set screws

 Miss Tisha,Good to see you are still active.
I thought that everyone knew about Bristol spline.... I have had a set since
about 1961.CheersR
    On Monday, June 15, 2026 at 11:14:00 PM EDT, Tisha Hayes via R-390
<r-390 at mailman.qth.net> wrote:  
 
 The R-390/ 390A use set-screws that are designed for a much higher torque
application.

It is known as a "Bristol-Spline" screw head. It may look like a hex or a
little like a TORX but the internals are all right-angles instead of
triangular or hexagonal faces.

The old Xcelite tool-set included Bristol-Spline bits, back in the day most
people had no idea what to do with the Bristol Spline bits.

The reason for Bristol-Spline is that when tightened it will not cam-out
(strip) like a hex bit will.

*Ms. Tisha Hayes, AA4HA*
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