What size torx key/bit/driver?
When buying a Torx bit set, the most common sets do not have the #27 bit in them and must be purchased separately.
Torx sizes are measured in multiples of 0.1mm, so a size of T20 is 2.0mm. Ideally you should find out the spec of the screw you're trying to undo to be sure you have the correct size torx key. If you don't know the size, you can try and measure it, but the stars in the screws tend to be quite small and quite hard to measure.The size is the diameter measured from the inside points of the star. So a measurement of 1.5mm would need a T15 key.
Tamperproof Torx
A security tamper-proof torx screw is the same shape as a standard torx screw, but it has a security point/pole in the middle. You'll need a tamper proof torx key that has a hollow center which will fit over the security pole of a fastener.
Standard Torx
A torx screw is similar to an allen/hex screw but instead of being hexagonal, it's a star shape. Any standard or tamperproof torx key, bit or driver will fit a standard torx screw.
From left to right in the above picture are the standard Torx, then the Torx security or tamper proof fastener, then the Torx plus with the rounded flutes and the last one on the right is another type security Torx.
Also see this post...
Torx Bits And Servicing - Harley Davidson Community
When buying a Torx bit set, the most common sets do not have the #27 bit in them and must be purchased separately.
A security tamper-proof torx screw is the same shape as a standard torx screw, but it has a security point/pole in the middle. You'll need a tamper proof torx key that has a hollow center which will fit over the security pole of a fastener.
A torx screw is similar to an allen/hex screw but instead of being hexagonal, it's a star shape. Any standard or tamperproof torx key, bit or driver will fit a standard torx screw.
From left to right in the above picture are the standard Torx, then the Torx security or tamper proof fastener, then the Torx plus with the rounded flutes and the last one on the right is another type security Torx.
Also see this post...
Torx Bits And Servicing - Harley Davidson Community