[R-390] Bristol Clamp Screws

[Jacques Fortin]

Barry and JK, the original screws for the "big knobs" clamps are 0.692 inches long.
See attached picture.
But the ones I still have are "eaten" in their internal splines.
The other that are assembled in the clamps in my picture are (more available) stainless hex ones.
Do not forget to have the small washer fitted in the clamp to prevent it to turn around when you try to tighten the screw(s).

73, Jacques, VE2JFE in Montreal

-----Message d'origine-----
De : r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> De la part de jkharvie via R-390
Envoyé : 15 juillet 2024 12:03
À : 72volkswagon at gmail.com
Cc : r-390 at mailman.qth.net
Objet : Re: [R-390] Bristol Clamp Screws



This is the screw, lock washer and square nutThe distance from the end of the screw to the socket head shoulder measures 0.508 inches Let me know if this works as a replacement.


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  On Mon, Jul 15, 2024 at 11:38, Barry Scott<72volkswagon at gmail.com> wrote:   ... and it just occurred to me that the smaller clamps may have shorter screws.  The screws for the large knob clamps are 9/16" long.  Is yours that long?
Thanks,Barry

On Mon, Jul 15, 2024 at 10:30 AM jkharvie <jkharvie at verizon.net> wrote:

Interesting!  I wonder if we have a collection of observed defected and other manufacturing irregularities.Yes, one screw surplus to my needs is yours, it is from a broken clamp that replaced with a split clamp configuration. Should be the size you need.John (N3JKE)




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  On Mon, Jul 15, 2024 at 10:41, Barry Scott<72volkswagon at gmail.com> wrote:   Looks like the front panel is about finished and turning my attention to
the knobs, escutcheon, and meter covers.

When I first removed the two large knobs a couple of years ago, I could tell one of the clamp screws did not have the same spline-drive as the other one as the socket was slightly larger than the other one.  I thought someone had replaced the spline-drive with a hex-drive but yesterday, I discovered that it is a larger spline socket.  Both are six-spline versions but one is a 0.096" (Xcelite 99-66) and the other is a 0.111" (Xcelite 0.111").

>From what I can tell, they're both #4-40 screws but one is just a few thousandths larger in diameter (not large enough to be a #5 and possibly just manufacturing tolerance differences).

Also, one knob has the two ribs in it and the other doesn't.  I didn't track which one had which screw in it and I don't think that really matters.  Most likely, somewhere in a repair depot, a knob was installed from a radio from a different manufacturer.

I'd like for these both to have the same Bristol drive (the 99-66 0.096"
version) so as to match the screws from all the other knobs.  Anyone know where I could get a proper socket-head screw for this?  I know these are pretty rare and likely the only place I'd find that is from another clamp/knob/radio but thought I'd ask.

Thanks,
Barry - N4BUQ
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