Thread Checking Tool

[MarkELynch]

Along with a caliper and thread pitch gauge here is a handy and inexpensive tool for every phonograph repairman. This tool will be able to answer most of the threading questions that we regularly receive on this board. It will only check external threads, the vast majority of thread types are listed. A few of the less common National “Special Threads” (NS) threads that Victor and other companies commonly used are not included. Notably 10-30 and 14-24. Victor generally used 14-24 on the bolts that attach the motor and the taper tube support to the board, also the bolts attaching the rear panels on the Orthophonic machines are 14-24. Edison used quite a few 5-40 fasteners and that is included on this steel tool. Victor used 10-30 on some set screws and some speed adjusting screws so get out your caliper and pitch gauges for these!

Available from Amazon and MSC.

https://www.amazon.com/Screw-Chekr-Thre ... 51HGOUZ91S

Mark

[JerryVan]

Mark shows a dandy device, but as he says, it doesn't include the odd threads used in some old phonographs.

This tool, along with a good caliper, or better yet, a micrometer, is essential for identifying any fractional, (i.e. not metric) thread. It's a thread pitch gauge...

https://www.amazon.com/dp/B075K368L3/re ... GhlbWF0aWM

Here is another excellent resource. If you can accurately measure the diameter of the thread, and identify it's pitch, you can identify the origins of just about any thread in existance. For example, if you have a screw that measures .073" diameter, and had 56 threads per inch, what size is it, (it's not ".073-56")? Looking at the chart, we see that it's a 1-56.

https://pages.cs.wisc.edu/~bolo/workshop/thread.html

[MarkELynch]

Jerry,

Thanks for the comprehensive screw size chart, it is nearly overwhelmingly complete. It doesn’t describe the various thread forms (Whitworth, Waltham, Acme, etc) but it lists what they are so they can be researched. In order for a screw to fit, the major diameter, pitch or TPI and thread form all must match. Fortunately the common fasteners on our machines are typical 60 degree NC, NF or NS Vee type threads.

Yes, I’m addition to the handy screw checker tool everyone should own a caliper and a thread pitch gauge. Thanks for the link to the pitch gauge. The handy screw checker gauge is a bit easier to use and will identify most threads on an old phonograph. I’d recommend it as the first stop when identifying a thread.

Mark