NPT internal and external thread gauges are marked with the words "upper, lower and base". After the thread gauge is screwed in, the internal thread is the end surface and the base surface is the standard, and it is qualified between the upper and lower parts. The plane of external thread at the small end is based on the datum plane, which is qualified between the upper and lower parts, and unqualified beyond the upper and lower parts.

If the customer has special requirements, the customer requirements shall prevail.

NPT thread: NPT thread is American standard 60-degree tapered pipe thread, which is divided into general sealed cylindrical pipe thread and general sealed tapered pipe thread, and the matching mode is "cone/cone" and "column/cone".

Thread ring gauge is used to measure the correctness of external thread size. The straight end is a whole, and the stop end is a whole. The stop ring gauge has a groove on the outer cylindrical surface. When the size is above 100 mm, the thread ring gauge is a double-handle thread ring gauge. Specifications are divided into coarse teeth, fine teeth and pipe threads. Thread ring gauges with pitch equal to or less than 0.35 mm and higher than secondary accuracy and thread ring gauges with pitch equal to or less than 0.8 mm have no end stop.

Inspection and judgment method:?

1, the threads of gauges and parts must be clean and free of burrs. The reference point is located at the end face of the part. The chamfer depth of the end face must exceed the minor diameter (bottom diameter) of the thread.

2. Check the thread with L 1 gauge; The thread end face is qualified between the maximum value (max) and the minimum value (min), otherwise the thread is judged to be unqualified;

3. After L1is judged to be qualified, check with L2 gauge. Check the screw with L2 gauge, if the thread end face is between the maximum value (max) and the minimum value (min), it is qualified, otherwise the thread is judged to be unqualified; The position of L2 gauge is 1/2t (pitch) of the position when L 1 gauge is inspected, that is, whether the L2 gauge is within 1/2t (pitch) is determined according to the position when L 1 gauge is inspected. That is, when L 1 gauge is at the maximum (max) position, L2 gauge (ring gauge) is qualified within the maximum+1/2t, and L2 gauge (plug gauge) is qualified within the maximum-1/2t; When L 1 gauge is in the position of benchmark B, L2 gauge (ring gauge and plug gauge) is qualified within the range of 1/2t of benchmark B. When L 1 gauge is in the minimum (min) position, L2 gauge (ring gauge) is in the minimum range of-1/2t.

4. The top gauge (taper gauge) should be used after L 1&L2 is judged to be qualified, and the taper gauge should not swing when it is put into the thread, otherwise it will be unqualified.