Eagle Products MR-3P Meter...

[a_strong]

Can anyone help me identify the thread used on the mounting studs of the Eagle MP-3P series of meter (82mm x 78mm). I require 4 fixing nuts.

I can say it is not M3, M3.5 is too big, 6BA is too small and the coarseness of the pitch would suggest it could be an American thread.

Any advice would be appreciated - Alan

[paulsherwin]

Most Eagle stuff was Japanese, if that's any help.

[Alistair D]

An awful lot of Eagle kit used American UNC threads.

From your description it will probably be 4-40 UNC

This link will help
http://mdmetric.com/thddata.htm

Incidentally 4-40 is the thread size used for the locking screws on old PC serial and parallel ports. Might help you confirm that is what you need.

Al

[a_strong]

Thanks Al and Paul - I expected the thread to be metric and although an M3 nut will engage the thread it locks up after approximately one turn. An M3.5 slips over the thread.

The locking nut from a PC card will engage the thread on the meter but again it locks up after approximately one turn. The diameter of the 4-40 UNC thread is more or less the same as that of the meter but the pitch is slighter finer.

I am reminded of a similar problem with Japanese meters when I was on the bench but I cannot remember how I overcame it, but then it was over 50 years ago!

A.

[WME_bill]

Radio threads for Eagle meter.
I suspect UNF4-48 or UNF6-40. Used a lot by HP and Tek.
I made up a comparison table for all the common radio threads, which I find makes matching threads much easier. You measure the outside diameter, and work out the threads per inch (TPI) by placing it side by side with a known BA or Metric bolt, with the threads interlocking.
I attach a copy of my table.
The threads are British Standard Whitworth, British Standard Fine, Model Engineers, British Standard Bicycle, British Association, UNified Fine, and UNified Coarse, ISO Metric coarse. Grouped by thread angle.
UNified and American National are effectively the same and interchangeable. The ISO Metric in a fine series is rarely seen.

Computers can be a bit misleading. PC usually use M3 for fixing the main board, and UNC4 -40 for the floppy drive and CD. However, often a M3 has been forced in, so the thread is damaged and will take either with difficulty. The original IBM PC used all UNC. wme_bill.

[a_strong]

Good morning Bill - I can say with certainty that the thread in question is not 4-40. I have found my tobacco tin of small US nuts and bolts among which are a number of 4-40 which mate perfectly with the serial/parallel port retaining screws but will not screw on to the meter thread.

I tried an M4 bolt alongside the meter mounting stud and it matches quite well, confirming that the thread pitch is very close to 0.7mm, or 36 (ish) tpi. M4 is of course a much bigger diameter.

I've not looked at your chart yet but from the measurements I have made I would say that a 7/64" x 36 tpi nut would fit but I have not been able to find such a nut in all the tables I have looked at since my first posting on the subject.

I also abandoned my Chinese vernier callipers in favour of my M&W micrometer and the o/d measures 0.108". Presto Tools (is also a Sheffield firm) so I will give their tech team a ring tomorrow and see what they come up with

I am also well into PCs and the vagaries of interchanging M3 and 4-40 threads at will.

Alan

[a_strong]

The mystery thread has been positively identified as a special extra coarse UN thread, UNS #4-36. It just so happened that there is a tap of that size on that well known auction site (item number:170884970993) which I have bought, and made four nuts.

So, problem solved and thank you to everyone who responded.

Alan - G3WXI.

[WME_bill]

UNS 4-36. I have never come upon that before. The only reference I can find says it is a special combination of diameter and pitch with pitch based upon a thread engagement of 9 times the pitch, but gives no other details.
So congratulations on your discoveries. wme_bill