M2.5 Metric Thread
Direct Answer
M2.5 is an ISO metric machine screw thread with a nominal major diameter of 2.5 mm and a standard coarse pitch of 0.45 mm. Requiring a 2.05 mm tap drill, it is the standard fastener for 2.5-inch SATA/SAS hard drive caddies, Raspberry Pi mounting standoffs, and consumer drone frames.
Source: ISO 68-1 / ISO 261 / DIN 13-1 / SFF-8201
Specs
| Nominal Major Diameter | 2.50 mm |
| Standard Coarse Pitch | 0.45 mm |
| Fine Pitch (Optional) | 0.35 mm |
| Tap Drill Diameter | 2.05 mm (75% thread engagement) |
| Minor Diameter (Internal) | 2.013 mm |
| Tensile Stress Area | 3.39 mm² |
| Common Drive Size | PH1 / T8 / 2.0mm Hex |
2.5-Inch Storage Drive and Server Caddies
The SFF-8201 specification mandates M2.5 metric threaded holes on the sides and bottom of all 2.5-inch form factor SATA SSDs, SAS drives, and enterprise server hot-swap drive trays. Using standard 6-32 PC case screws in an M2.5 drive hole will permanently strip the aluminum threads.
Single-Board Computer Standoffs
All modern Raspberry Pi models (Model B+, Pi 2, Pi 3, Pi 4, Pi 5) feature standardized 2.7 mm mounting corner holes designed specifically for M2.5 brass or nylon hex standoffs.