A Torx insert screw is the small screw that clamps a carbide insert into its holder. Its size is written as thread diameter x length in millimetres, for example M2.5 x 6, M3.5 x 10 or M4 x 10, and each thread size normally takes one Torx key size: roughly T6 for M2, T7 for M2.5 and T15 for M3.5 and M4. Makers do not all agree, so check the key size against the screw head.
What an insert clamping screw is
On many turning, boring and drilling tools, the insert has a centre hole and a screw passes through it into the holder. Tightening the screw pulls the insert against the seat. These screws have a six-lobe (Torx) drive.
How the size is written
The first number is the thread diameter, shown with an M for metric. The second is the length. M3.5 x 10 is a 3.5 mm thread, 10 mm long. Order the length your holder uses: the same thread can come in several lengths.
Which Torx key goes with which thread
The table below is taken from maker and catalogue listings for insert screws. Where listings differ, the range is shown.
| Thread |
Torx key seen in listings |
| M2 |
T6 |
| M2.2 |
T7 |
| M2.5 |
T7 (one listing shows T8) |
| M3 |
T9 to T10 |
| M3.5 |
T15 |
| M4 |
T15 |
Some makers use Torx Plus (marked IP or TP), which is a different profile from standard Torx; a standard T key is not a substitute. Always read the key size on the screw head or in your holder's parts list before ordering.
Why a worn key strips screws
A Torx drive spreads the force over six lobes, which works only when the key fits snugly. A worn or wrong-size key has play in the recess, so it can slip and round the lobes. Replace keys whose tips look rounded, and push the key fully into the recess before turning.
What BVF sells
Each product below is a pack of 10. The sizes are the product's own listed options (thread diameter x length, mm). Each size is also listed in a High Precision version with the same options.
| Product |
Listed sizes |
| Torx Screw 2 mm (Pack of 10) |
2 x 5, 2 x 6 |
| Torx Screw 2.2 mm (Pack of 10) |
2.2 x 5, 2.2 x 6 |
| Torx Screw 2.5 mm (Pack of 10) |
2.5 x 6, 2.5 x 8 |
| Torx Screw 3 mm (Pack of 10) |
3 x 10, 3 x 12 |
| Torx Screw 3.5 mm (Pack of 10) |
3.5 x 10, 3.5 x 12 |
| Torx Screw 4 mm (Pack of 10) |
4 x 10, 4 x 12 |
| Torx Flag Key T6 / T7 / T8 / T10 / T15 (Pack of 10) |
T6, T7, T8, T10, T15 |
All of these, and the High Precision versions, are in the Torx Screws & Keys collection.
What to check
- Read the thread and length on your old screw or the holder's parts list, then pick the same size.
- Pick the key that matches the drive, using the table above as a guide.
- Check that your key is not worn at the tip before you turn the screw.
Related collections
