T-nuts are as the title says, a nut with a “T” cross-section. This means they can be used in a T-slot for retaining and fixing parts.
The T-nut fits in a T-slot and so has to be made to certain dimensions.
Below I have labelled the dimensions of a T-nut and in the table I have given some of the common sizes.
| Slot Size B [mm] | Thread A | C [mm] | D [mm] | E [mm] | F [mm] |
| 8 | M6 x 1.0 | 10 | 6 | 14 | 19 |
| 10 | M6 x 1.0 | 11 | 6 | 16 | 22 |
| 10 | M8 x 1.25 | 11 | 6 | 16 | 22 |
| 12 | M10 x 1.5 | 13 | 7 | 17 | 22 |
| 14 | M10 x 1.5 | 16 | 9 | 22 | 29 |
| 14 | M12 x 1.75 | 16 | 9 | 22 | 29 |
| 16 | M12 x 1.75 | 16 | 9 | 25 | 29 |
| 18 | M16 x 2.0 | 19 | 11 | 29 | 32 |
| 20 | M16 x 2.0 | 25 | 14 | 32 | 38 |
| 22 | M20 x 2.5 | 25 | 14 | 35 | 38 |
| 27 | M24 x 3.0 | 29 | 18 | 41 | 51 |
I have found that in the model making arena the T-nut dimensions are not that accurately followed. Sometimes a mix of T-nuts and threads is actually rather useful.
Double T-nuts that I made from mild steel for my low profile vice project.
These are 12mm T-nuts and I have threaded them for 6mm and 8mm.
Long T-nuts that I made to extend the working diameter of the rotary table.