Kyosho 1-S34025H M4x25mm Hex Flat Head Screw 5pcs

A pack of five M4 x 25mm flat head screws with a hex socket drive, from Kyosho's universal hardware range.

M4 is a step up from the M3 fasteners used across most of a radio control chassis, and it appears where loads are genuinely high: engine mounts, main chassis fixings, and the structural joints on larger 1/8 scale cars. Using an M3 where an M4 belongs is a good way to shear a screw under load.

The flat countersunk head sits flush with the surface rather than standing proud, which keeps nothing catching on the ground and lets parts sit directly against each other. It requires a countersunk hole, so it is not interchangeable with a button or cap head in the same position.

The hex socket drive lets you apply real torque without rounding the head, which matters more at M4 because the torque figures are higher.

At 25mm this is a long screw for passing through several parts before threading in. Note the pack contains five rather than ten, which is normal for the longer and larger sizes. This supersedes the older Kyosho number 1412.