Hex Flat-head Screw M2-M5 (Stainless Steel) -wss

Flat and Button Socket Cap Screws
Flat socket head cap screws are used when the top of the screw head is to be flush with one of the assembly surfaces. The underside of the screw head and the accompanying hole are countersunk at an 82-degree (includes angle). Flat socket head cap screws are preferred over slotted flat head cap screws if assembly and disassembly are frequent because the drive is less likely to strip with repetitive use.

Button socket cap screws are the fastener of choice if the screw head is outside of the assembly, there are clearance issues, and a socket drive is desired. Button sockets are not meant to handle as much stress as a socket head cap screw as the heads have less "beef".