| Code | Description | Milling ( M ) | Turning ( T ) | Corollary info |
|---|---|---|---|---|
| M00 | Compulsory stop | M | T | Non-optional—machine will always stop upon reaching M00 in the program execution. |
| M01 | Optional stop | M | T | Machine will only stop at M01 if operator has pushed the optional stop button. |
| M02 | End of program | M | T | No return to program top; may or may not reset register values. |
| M03 | Spindle on (clockwise rotation) | M | T | The speed of the spindle is determined by the address S, in surface feet per minute. The right-hand rule can be used to determine which direction is clockwise and which direction is counter-clockwise. Right-hand-helix screws moving in the tightening direction (and right-hand-helix flutes spinning in the cutting direction) are defined as moving in the M03 direction, and are labeled "clockwise" by convention. The M03 direction is always M03 regardless of local vantage point and local CW/CCW distinction. |
| M04 | Spindle on (counterclockwise rotation) | M | T | See comment above at M03. |
| M05 | Spindle stop | M | T | |
| M06 | Automatic tool change (ATC) | M | T (some-times) | Many lathes do not use M06 because the T address itself indexes the turret. Programming on any particular machine tool requires knowing which method that machine uses. To understand how the T address works and how it interacts (or not) with M06, one must study the various methods, such as lathe turret programming, ATC fixed tool selection, ATC random memory tool selection, the concept of "next tool waiting", and empty tools. These concepts are taught in textbooks such as Smid,[1] and online multimedia (videos, simulators, etc); the latter are usually paywalled to pay back the costs of their development. They are used in training classes for operators, both on-site and remotely (e.g., Tooling University). |
| M07 | Coolant on (mist) | M | T | |
| M08 | Coolant on (flood) | M | T | |
| M09 | Coolant off | M | T | |
| M10 | Pallet clamp on | M | For machining centers with pallet changers | |
| M11 | Pallet clamp off | M | For machining centers with pallet changers | |
| M13 | Spindle on (clockwise rotation) and coolant on (flood) | M | This one M-code does the work of both M03 and M08. It is not unusual for specific machine models to have such combined commands, which make for shorter, more quickly written programs. | |
| M19 | Spindle orientation | M | T | Spindle orientation is more often called within cycles (automatically) or during setup (manually), but it is also available under program control via M19. The abbreviation OSS (oriented spindle stop) may be seen in reference to an oriented stop within cycles. |
| M21 | Mirror, X-axis | M | ||
| M21 | Tailstock forward | T | ||
| M22 | Mirror, Y-axis | M | ||
| M22 | Tailstock backward | T | ||
| M23 | Mirror OFF | M | ||
| M23 | Thread gradual pullout ON | T | ||
| M24 | Thread gradual pullout OFF | T | ||
| M30 | End of program with return to program top | M | T | |
| M41 | Gear select - gear 1 | T | ||
| M42 | Gear select - gear 2 | T | ||
| M43 | Gear select - gear 3 | T | ||
| M44 | Gear select - gear 4 | T | ||
| M48 | Feedrate override allowed | M | T | |
| M49 | Feedrate override NOT allowed | M | T | This rule is also called (automatically) within tapping cycles or single-point threading cycles, where feed is precisely correlated to speed. Same with spindle speed override and feed hold button. |
| M52 | Unload Last tool from spindle | M | T | Also empty spindle. |
| M60 | Automatic pallet change (APC) | M | For machining centers with pallet changers | |
| M98 | Subprogram call | M | T | Takes an address P to specify which subprogram to call, for example, "M98 P8979" calls subprogram O8979. |
| M99 | Subprogram end | M | T | Usually placed at end of subprogram, where it returns execution control to the main program. The default is that control returns to the block following the M98 call in the main program. Return to a different block number can be specified by a P address. M99 can also be used in main program with block skip for endless loop of main program on bar work on lathes (until operator toggles block skip). |