The machinability index is relative ease of machining a metal.
American Iron and Steel Institute rated AISI 1212 steel which is equivalent to EN1A in the UK as 100%. This sets a baseline from which you can compare the machinability of different materials.
| Free-cutting Brass | 300% |
| Aluminium 6063T | 190% |
| AISI 1212 (EN1A) | 100% |
| Naval Brass | 90% |
| 303 Stainless | 65% |
| AISI 1040 (EN8) | 64% |
| Phosphor Bronze | 60% |
| Inconel | 30% |
| Nimonic 90 | 9.1% |
Free Machining Steels
A group of steels designated as being easy to machine. Contain one or more additives, which enhance machining characteristics and lower machining cost.