A button head screw has a low, rounded head with a hex socket in the top. It sits lower and looks tidier than a standard cap screw. These are M3x6 in black alloy steel, so they blend into a black 3D printed case, a dark panel or a black PCB.
They're for indoor builds. The black finish is thin, so outdoors or anywhere damp they can rust. For outside, use the 304 stainless M3x6 instead. The 6mm length is the thread under the head, which is enough to go through a 1.6mm PCB into a nut, or to hold a lid onto a heat-set insert.
Specifications
Choosing and fitting
- Check the length
Through a 1.6mm PCB into a standoff, 4.4mm of thread goes in, so the standoff needs a thread at least that deep. Through the same PCB with an M3 hex nut on the back, about 2mm shows past the nut.
- Use a 2mm hex key
Button heads take a 2mm hex key, one size down from the 2.5mm key an M3 cap screw takes. Push the key all the way into the socket and stop once the screw is snug. The socket is shallow, so a key that slips or a lot of force will round it out.
- Into plastic, fit an insert first
An M3 thread cut straight into a 3D print holds at first, then wears loose after the screw has been in and out a few times. Fit an M3 heat-set insert and the screw goes into brass instead.