Identify the test point already fitted to your machine

A diagnostic connection is specified from two independent ends: the connection presented on the outside, and the port thread that screws into the machine. One M16×2 test end is supplied on a whole range of port threads, so the outside half tells you nothing about the inside half. Work from measurements rather than from the series name on an old invoice.

Step 1 — measure the pitch on the test end

M16×2 and M16×1.5 look the same across a workshop and will not mate. Lay a rule along the thread, count a whole number of threads, and read the length they span. Ten threads is easier to read accurately than one.

Step 2 — cross-reference the series name you were given

What still has to be confirmed

End What to read Why it is read separately
Outside, the test end Nominal diameter and pitch, or the stamp on the body or cap It identifies the interface family, not the pressure class
Inside, the port thread Thread family: BSPP, NPT, metric, JIC, UNF The pressure rating follows the port thread, not the test end