Seeking Specs for B&S J Tap

I have an older Federal back plunger indicator that has a threaded boss on the side. I sent a message to Mahr/Federal and asked them what the thread size was and they replied 'B&S "J" Tap - .156 Tap NO. 10159-10'. Searches for something that matches that turned up nothing.

A 0.155" gage pin fits the through hole well. Also, an 8-36 gun screw threads into it without binding but is very loose. I'm guessing that the threads might be 10-36. However, 36TPI is very close to 0.7mm pitch and that through hole is about right for an M5 screw so it could be M5-0.7 which is non-standard.

Does anyone have any idea what the specs are on that B&S J tap? I sent a message back to Mahr earlier this morning asking the same and I'm awaiting the reply.

IIRC / a bells ringing but it's foggy, 5mm dia x 0.75 mm pitch is an old (like pre WW II) German DIN thread and as Mahr is a German outfit .???????

FYI Victor do that tap for $5.10 Metric Taps - Taper, Plug, Bottoming, and Spiral Point - millimeter sizes.

The die is $9.50 Metric Dies | Adjustable, High Speed, & Round Dies


FWIW I came across that thread on the instruments of a pre war car ........................ I think???? it was a Talbot (original French built not the modern Chrysler rubbish)