What is the name/type of the Apple IIc case screws?

Question

My Apple IIc is what appears to be the first US model: A2S4000 with version 255 ROMs. The upper half of the case is held to the base with six Phillips drive button-head 2 cm screws with a very wide thread, of which I'm missing two. They look like this:

Larger images: bit, head.

The front four screws going through the keyboard tap straight into plastic sleeeves molded into the case, so there's a danger of destroying the existing threads of I use the wrong screw (which obviously I want to avoid). The rear two screws go through a hole in a plastic tab with a small piece of thin sheet metal, with two similar holes, folded around it, so I am guessing that this would conform with screws with a different pitch.

What are these screws called, or what terms should I use when searching for replacements? What are the dimensions I should be confirming (I'm likely to be ordering these over the Internet) and, if you don't already know what dimensions Apple specified for this screw, how ought I measure them?

Answer 1

What are these screws called

Exact term may depend on manufacturer, but usually they are classed as single threaded, self-tapping with thread-forming as sub-class. The tip shown is close (*1) to a Type B Tip indicating that it's meant to be used with a predrilled hole of about the same diameter as the inner one of the screw.

Applicable standards are DIN 7981 / ISO 7049 (old) or DIN/ISO 1478..1483 (new).

If your intention is to get exact replacement to avoid recutting, it may need some luck and a good way to measure the valid parameters (inner/outer diameter, thread inclination, thread form), as these screws are usually odered in a more relaxed manners than bolts are. After all, their counterpart is a metal/plastic hole, it'll cut the way it needs on its own and it's not intended to be opened or used again - or at least not many times.

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*1 - Close, as there is almost no cone at the tip - still within the definition.

Answer 2

They are self-tapping but not self-drilling (the tip is also blunt.)