Specification description:
Size = inner diameter x thread pitch x length, 2D = 2 x inner diameter
Example of a specification: M3 x 0.5 x 2D
M3 (inner diameter D is 3 mm)
0.5 (tooth pitch after installation is 0.5 mm)
2D (length after installation is 2 x D = 2 x 3 = 6 mm)