Thread Standard and Type

R, PT, BSPT -- 55° Taper Pipe Thread Metric Thread
R1/8 R1/4 R3/8 R1/2 M5 x 0.8 M6 x 1 M8 x 1 M10 x 1 M12 x 1.25 M14 x 1.5 M16 x 1.5 M20 x 1.5

UNF NPT -- 60° American Standard Taper Pipe Thread
10-32 UNF 1/8 NPT 1/4 NPT 3/8 NPT 1/2 NPT