All The Toolbits We Supply Are Manufactured In The UK Rectangular toolbits are supplied with square ends Rectangular Toolbits are made to h12 tolerance M42 high speed steel is a cobalt molybdenum grade with a high hardness and superior hot hardness offering excellent cutting performance and excellent wear resistance. These 8% cobalt high speed steel type M42 tool bits are suited for tougher materials such as work hardening types. They offer increase tool life with retention of the cutting edge. M42 toolbits are supplied hardened to approximately 65 to 68 HRC Typical analysis - Cobalt - 8% Carbon - 1.05% Molybdenum - 9.5% Vanadium - 1.15% Chromium - 3.75% Tungsten - 1.5% Silicon - 0.35% We also supply special sizes which are not listed. If the size you require is not listed please contact us for a quote.