Thread run-outs & undercuts
An M10 external thread running up to a shoulder takes a normal undercut 3.2 to 5.2 mm wide, Ø 7.7 mm h13, with r 0.8: the groove the threading tool runs out into so it never reaches the shoulder. Type or pick the thread below and choose the external or internal member: the Make tab gives the run-out, the undercut’s width, diameter and corner radius in the normal and short forms, drawn for that size.
The values are DIN 76-1’s, by pitch: the undercut diameter is the thread’s nominal Ø less k (external) or plus k (internal). ISO 3508 and ISO 4755 cover external threads only and are listed for comparison.
Normal or short form?
Use the normal form (Type A external, Type C internal) unless there is a technical reason not to. The short form (Types B and D) leaves the tool less room to run out and needs special tools, so the drawing should ask for it.