Does any have suggestions for the size/type of screws to use when converting a Pyraminx to a Tetraminx, or when building an Octaminx?

The sorts in my Pyraminx appear to be some form of specialty screw; machine screw heads, extremely long unthreaded shafts, and just a bit of shallow threading at the tips. The local hardware shops don't seem to have any obvious matches for what's needed (something shorter that won't unscrew over time).

I recall seeing instructions for this conversion in an old book on "Solving the Pyramid Puzzle", including photos of a disassembled and a transparent Pyraminx. Does anyone have it handy, or does it suggest replacement screws?

I tried the same thing. Yes, the screws appear to be special. I ended up using sheet metal screws with washers on the heads. (Sorry, I don't know what size they were, but I'm sure that they were pretty standard sizes.) The most difficult part is starting and keeping the screws straight. I did succeed in making a tetraminx, but it seemed sloppy and often fell apart for this reason. I finally broke down and bought a tetraminx from Meffert's. Now my cobbled-up tetraminx is in my rainy-day spare puzzle parts bin.

I've made 2 so far. One normal and one bandaged.
I used bolt cutters on the back of my pliers to cut the bolts. I cut about halfway up the threaded part of the screw. The tip flattened a bit when I cut, but it didn't seem to hurt anything.

I also put a few drops of super glue in the hole but that may be optional.

Both mine work great and haven't fallen apart yet.

Unless my pyraminx was different then yours (I used Meffert's packaged by Think Puzzles), I don't understand how you could only remove 1/2 of the threaded portion and still make the screw short enough to keep its head in the hole below the surface of the removed pyramid tip. My screws only had a very short length of thread near their tip.

I guess I could have removed all of the threaded length (and then some) and then used superglue to hold them from backing out. I suspect, however, from its looks that the center ball was made from polypropylene/Delrin (same as plastic milk cartons) which is a very difficult material to glue to.

Doug.

Both mine were older models made by Tomy. The bottom half of the screw was threaded while the other half was bare. I cut 1/4 of the entire length of the screw.

If your threads aren't as long, I can see how this wouldn't work. Sorry.