I notice that the cases for CDROM drives etc. used in PCs are constructed of relatively thin sheet metal (1/32" perhaps) yet are able to support M3x.5 machine screws. The hole for the screw has what looks like a 1/16" - 1/8" long threaded tube on the inside of the case that basically supports most of the screw threads. Is this done with a special tool or is this "tube" brazed over the hole then tapped? Normally, if one uses a sharp drill bit then taps anything 1/32" thin there is very little thread to support a machine screw regardless of the TPI.