I Need Help With Tapping Holes For 6-32 and M3 Screws: Confused With The Dimensions

[nawk]

I am very confused about the dimensions for the UTS 6-32 and M3 described in the following 2 tables:
http://en.wikipedia.org/wiki/Unified_Thread_Standard
http://www.tribology-abc.com/calculators/metric-iso.htm

I measured the major diameter of a standard (6-32) screw commonly used in PCs in the picture below,


and find that it is less than ~3.5052mm.

Could someone please tell me how to tap a hole for these two type of screws?

Thanks,
nawk

[anachlores]

Well first, you need the correct tap. You can buy then in the "tap and die" section of home depot, OSH, lowes, etc.
Then you need to take the material into account. if it is sheet metal, then you will need to punch the hole in. If it's acrylic, thicker metal, magical fairy hide (O.o) then you can tap it with a pilot hole directly. The taps should come with a guide for telling you how big to make the pilot hole, then you just tap it slowly, backing it out every few revolutions and use some oil or water. For this size, clean the tap whe you back it out, or bad things may happen....

For thin sheet metal, drill a REALLY small hole, punch it through with god knows what, then tap into that. If you look at your case, you'll be able to see what I am talking about, the screw goes into a hole that has been "mushed" so it is thicker than the actual material.

edit

Also, there are threaded inserts available if you cannot, or don't feel up to tapping. I have heard great things about helicoils for sheet metal use.

[nawk]

Getting the correct tap is what I am concerned about. As you can see, the screw in the picture is a common screw found in PC assemblies. According to the wiki article this kind of screw is referred to as a UTS 6-32. Details indicate that it's got a major diameter of 0.1380 inches (equivalently 3.5052mm) but after measuring the major diameter myself (as you can see in the picture above) it's more like 2mm.

Am I not understanding correctly? Could someone who've tapped holes for these types of screws UTS 6-32 and M3 please tell me which tap to use?

I basically need to drill and tap four holes in the aluminum h.d.d cage for the Lian Li EX-H34S enclosure.

Thanks,
Nawk

[Waterlogged]

Don't worry about major diameter so much. For starters, your measuring the end of the screw which hardly is ever to spec for these types of screws. . .secondly, your links fail to mention any tolerancing in the charts, which there is always something. Just use the drill sizes specified for the sizes you plan on using and a "plug" tap and you'll be fine.


btw, my credentials are "former machinist of 12 years".

[CrazyNutz]

You just need a 6-32 tap, and drill set (has the tap, and the correct drill bit). Get it at your local hardware store.

[OldChap]

If the metal that you are trying to tap is very thin (or even if it is not) then you might consider Rivnuts. Similar to fit as a pop rivet but once fitted already has the thread ready for those screws