What is the difference between M2 and M35 drill bits ?

The most popular HSS drill bits fall into the following two categories: M2 & M35.  Depending if you are drilling mild steel or hardened steel will determine whether you purchase M2 or M35 drill bits. Cobalt M35 drill bits will do everything the M2 bit can do, and more – M35 HSS drill bits will drill through hardened steel like stainless as well as mild steel and cobalt ensures the bit is heat resistant. M35 bits keep long lasting cutting edges and will not dull easily 

The M2 bit is best for everyday use like milder steel, plastics, fibreglass, drywall and wood (although a specialised wood bit is better). However, the M2 bits can lose their sharpened edge quicker than cobalt bits and will not last as long as M35 cobalt bits