Sizes 3mm are manufactured from un-hardened silver steel, 4mm and above are high quality case hardened mild steel.

Tolerances:
3mm = +0.002
+0.008

4 - 6mm = +0.004
+0.012

8 - 10mm = +0.006
+0.015

12 - 16mm = +0.007
+0.018.