Kyosho 1-S53003 M3x3mm Set Screw 10pcs

A pack of ten M3 x 3mm set screws, from Kyosho's universal hardware range.

A set screw, also called a grub screw, is headless. The whole body threads into the part, so nothing protrudes above the surface. That is what makes it the right fastener for locking a component onto a rotating shaft: a pinion gear onto a motor shaft, a collar onto an axle, a clutch bell onto its pilot. A protruding head on a spinning part would catch on everything around it.

They work by pressing their tip directly against the shaft, and that means installation matters. Most shafts have a machined flat for the screw to seat against, and a set screw tightened onto the round part of a shaft will work loose or damage the shaft. Thread lock is normally used because vibration backs them out readily.

They are also easy to lose, being small and headless, and a pinion that has lost its grub screw usually strips the spur before you notice.

At 3mm this is a short screw for shallow bosses. This supersedes the older Kyosho number 1161.