M5 Metric Thread
Direct Answer
M5 is an ISO metric machine screw thread with a nominal major diameter of 5.0 mm and a standard coarse pitch of 0.80 mm. Requiring a 4.20 mm tap drill, it is the universal standard for bicycle water bottle cages, disc brake rotor mounts, and 2020/4040 aluminum extrusion T-slot framing nuts.
Source: ISO 68-1 / ISO 261 / DIN 13-1 / ISO 4210
Specs
| Nominal Major Diameter | 5.00 mm |
| Standard Coarse Pitch | 0.80 mm |
| Fine Pitch (Optional) | 0.50 mm |
| Tap Drill Diameter | 4.20 mm (75% thread engagement) |
| Minor Diameter (Internal) | 4.134 mm |
| Tensile Stress Area | 14.2 mm² |
| Common Drive Size | 4.0mm Hex / T25 / PH2 |
Bicycle Engineering Standard
M5×0.8 mm is the most prevalent fastener on modern bicycles (ISO 4210). It secures water bottle cages, fender eyelets, rear pannier racks, and 6-bolt disc brake rotors (which mandate Torx T25 M5 screws with pre-applied threadlocker).
T-Slot Extrusion Modular Framing
In modular industrial framing (2020, 2040, 4040 aluminum profiles), M5 button-head and socket-head screws paired with drop-in M5 hammer nuts / roll-in spring nuts are the standard interconnect for CNC routers, 3D printer frames, and laboratory benches.