To identify a foreign thread, first you must identify whether it is parallel or tapered. Then you can measure the thread pitch in millimeters across the thread crests using a gauge.
Next you must identify the OD (outside diameters) of the fitting using calipers. If the thread is parallel place the calipers over the threads to determine the OD. For tapered threads, since the first two rows are tapered, you must place the calipers over the third row from the end of the fitting.
Metric Thread Callout System
Once you have identified the OD and thread pitch, you can combine both to determine the metric thread callout. For example a thread with an OD of 2.0 millimeters and a pitch of 30 millimeters, the metric thread callout would be M30 X 2.0.
TUBE NUT PART #
CUTTING RING PART #
TUBE PLUG PART #
TUBE CAP PART #
4 mm 6 mm 8 mm 10 mm 12 mm
8 mm x 1.0 10 mm x 1.0 12 mm x 1.0 14 mm x 1.0 16 mm x 1.0
5201LL-04 5201LL-06 5201LL-08 5201LL-10 5201LL-12
5202LL-04 5202LL-06 5202LL-08 5202LL-10 5202LL-12
6 mm 8 mm 10 mm 12 mm 15 mm 18 mm 22 mm 28 mm 35 mm 32 mm
12 mm x 1.5 14 mm x 1.5 16 mm x 1.5 18 mm x 1.5 22 mm x 1.5 26 mm x 1.5 30 mm x 2.0 36 mm x 2.0 45 mm x 2.0 52 mm x 2.0