Tubing gauges are used to detect the internal threads of oil casing according to the Petroleum Institute (API) standard.

CSG (short circular thread casing, with circular threads and arc-shaped tooth tops and bottoms); The taper is 1:16; The tooth profile angle is 60 ° and the tooth flank angle is 30 °; The pitch is 3.175 and 2.54, the tooth profile height is 1.810 and 1.412, with 8 and 10 teeth per inch, respectively. The code for the long thread sleeve is LCSG. BCSG (trapezoidal threaded sleeve, with a taper of 1:16 for sizes below 133/8 inches and 1:12 for sizes above 16 inches, and a pitch of 5.08 (5 teeth/inch); The tooth height is 1.575; The tooth flank angles are 3 ° and 13 °, and the tooth profile angle is 13 °.

Note: For threads below 133/8 inches, the top and bottom of the teeth should be parallel to the busbar; Above 16 inches, the thread tooth top and bottom are parallel to the axis.

The commonly used specifications for CSG include 41/2CSG, 5CSG, 65/8CSG, 7CSG, and 75/8CSG.

The commonly used specifications for LCSG include 41/2LCSG, 5LCSG, 65/8LCSG, 7LCSG, and 75/8LCSG.

The commonly used specifications for BCSG include 41/2BCSG, 5BCSG, 65/8BCSG, 7BCSG, and 75/8BCSG.