Traditionally there were three thin-thread screws on the PC: one with 7/32” hex head and 5 mm in length – used to fasten optical drives and I/O brackets to the case –, another with a round head and the same length, 5 mm – used to fasten the motherboard to the case –, and a third one also with a round head, but shorter, with 4 mm in length – used to fasten the floppy disk drive to the case. These three traditional thin-thread screws are pictured on Figure 7.

click to enlarge
Figure 7: Traditional thin-thread screws.

Since they all use the same thread, you can fit a 5 mm-long screw where a 4 mm-long should be used, so play close attention. As mentioned, 4 mm-long screws must be used to fasten floppy disk drives to the case.

Using 5 mm-long round head screws where 5 mm-long hex head ones should be used doesn’t make any difference. The real problem is the length, not the shape of the head.

We also said that I/O brackets should be fastened using thin thread hex head screws. Well, this isn’t always true; this will depend on the case. There are cases that require thick-thread hex head screws to be used, others require thin-thread hex head screws, and there are cases that don’t require any screw at all to fasten the I/O brackets.

The same goes for the screws used to fasten the motherboard to the case. Some cases will require thin-thread screws, some will require thick-thread screws and some will not require any screw at all. We will talk more about that on the next page.

You can find more thin-thread screws than the ones we shown on Figure 7 (the first one on the left on Figure 8 and on the right on Figure 9 is the traditional hex head thin-thread screw, for comparison). Usually screws like these come with the optical drive.

click to enlarge
Figure 8: Other thin-thread screws you may find.

click to enlarge
Figure 9: Same screws, view of their heads.

All thin-thread screws should be screwed using a #1 Phillips screwdriver.