Designation of Screw Threads

Designation of Screw Threads Points : Designation of Screw Threads According near Indian standards, IS : 4218 (Part IV) 1976 (Reaffirmed 1996), the whole description of screw thread shall contain 1. Size designation The dimension of screw thread is chosen by the letter `M' follows by diameter with pitch, the two being divided by the sign ×. As there is no sign of pitch, it means that a coarse pitch is disguised. 2. Tolerance designation. This shall include (a) A form designate tolerance grade as indicate under:
7 for fine grade, 8 for normal (medium) grade, and 9 for coarse grade.

(b) A letter choose the tolerance place as indicate below:
H for unit thread, d for bolt thread with allowance, and h for bolt thread with no allowance.

For instance Bolt thread of 6 mm size of coarse pitch and by allowance on threads with normal (medium) tolerance grade is designated as M6-8d.