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, which suits lids and covers that stay on show. These are M3 screws in 304 stainless steel, sold per screw in two lengths, M3x4 and M3x6.
You can use them to screw a board down onto M3 standoffs, or to close a 3D printed case that has M3 heat-set inserts. The length is the thread under the head, so M3x4 suits a board screwed straight into a standoff and M3x6 suits a board or thin panel with a nut on the back. 304 stainless copes with damp and outdoor use, so they suit a weatherproof box as well as an indoor build. For a dark finish there is also an M3x6 in black alloy steel.
Specifications
Choosing and fitting
- Work out the length
Add up what the thread has to pass through. Through a 1.6mm PCB into a standoff, M3x4 leaves 2.4mm of thread in the standoff, about five turns. Through the same PCB with an M3 hex nut on the back, use M3x6: the nut is 2.4mm thick, so about 2mm of thread shows past it.
- 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.