Rod Size for Die Threading

Thread Specification:

Examples:

#10-32 10-32	In	Numbered machine screw thread (#1 through #12)
1/4-20 1/4"-20 0.25-20	In	Fractional UNC thread (1/4" through 1")
1/2-20 1/2"-20 0.5-20	In	Fractional UNF thread (1/4" through 1")
M6 M6x1 6x1	mm	Metric coarse thread (M1 through M22)
M6x0.75 M6x.75 6x.75 6mm x.75	mm	Metric fine thread (M1 through M22)
0.255-40 .255-40 0.255"-40	In	Non-standard thread (0.06" through 1.0")

Reducing the size of a rod you want to thread with a die makes it easier to start the die,
but the real secret is to add a 30° chamfer to the end of the rod.

Die Blank Size is the Major Diameter less 10% of the Pitch.
This is about the same as common bolts.