The screws used for devices are actually 6/32. 8/32 screws are used for octagon and 4-square boxes to mount light fixtures or blank plate/mud ring. 6/32s are for switches and plugs as well as faceplates. 10/32 is the size for green grounded screws used in metal boxes. 10/32 is also used on some metal fan-rated boxes and outdoor cast aluminum round boxes.
Oops! sorry fluorescent lover 40 for the wrong information
I work on computers and just tested that the 6/32 case/Hard Drive screws thread properly onto the devices faceplate screw and like wise the face plate screws will thread into a hard drive so I guess I was wrong. I usually don't work with electrical boxes but I did build a extension cord box with 7 outlets and a switch (4 gang box with 3 standard duplex receptacles and one switch/outlet combo). again sorry for the incorrect information