Upon exploring ways to silence the loud fan in my DMM6500, I opened the device and discovered that one of the four small screws holding the case had a damaged head. I probably did not notice that before, because it was hidden by the rear rubber bumper. Since I have no experience with non-metric screws and the associated terminology, I am kind of stuck determining the precise type of the screws to find a replacement. In addition to that, the screws have a strange countersunk head that I have never seen before. So far, a caliper and the internet have made me believe that it could be something like #4-40 x 1/4 UNC undercut countersunk phillips machine screw. Can anyone here verify that?
I also need the thread type of the bigger screws holding the fan, the front panel and the rectifier. However, the manual mentions that the screw holes for mounting the DMM6500 to a rack require #6-32 UNC screws and the screws in question seem to fit those holes.
I have attached an image of both screw types.