[Collins] 75A-2 tuning shaft collar set screw thread (and source)?

[Gerald]

On Fri, 2005-08-19 at 14:30 -0400, Christopher J Galbraith wrote:
> Hi gang,
> 
> I am replacing the tuning shaft on a 75A-2 that was bent in shipping.
> The original had a pin securing the 10-turn stop's collar on the tuning
> shaft.  Luckily, the collar is also tapped for 2 set screws, so the
> replacement shaft can be a simple section of 1/4" stainless steel round.
> 
> 
> The problem is, I don't know what the thread size is and I haven't found
> a match at the local hardware store (in either a set screw or a machine
> screw).  I think it might be 3-48 or 4-48 (definitely a finer pitch than
> 4-40) but I have not found a fastener to check this.
> 
> Does anyone happen to know (or can make a good guess) at the thread
> diameter/pitch of the set screw threads on the tuning shaft collar for
> the 10-turn stop on the 75A-2/3?
> 
> Also, does anyone know a source of this set screw in quantities of 10 or
> less?
> 
> Thanks very much for any help,
> 
> 73, Chris KA8WFC

3-56 and 4-40 are the fine threads of those sizes. Hardware stores
sometimes have 4-36 and less often 3-48 which are the coarse sizes.

3-48 were used to hold bottom and top covers of Command sets of WW2 vintage.

My McMaster-Carr catalog shows 4-40 as coarse and 4-48 as fine. Under
taps they show 4-36 as special. Must have been a change in standard that
I've missed. I still prefer 4-40 to 4-36 as I have for a long time.

A hobby shop may have ordinary and sometimes set screws in the fine
threads as used for radio controlled cars. Small Parts in Florida will
surely have them but buying them by the 100 from McMaster-Carr
(www.mcmaster.com) may be cheaper after paying shipping..
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer