I've bought Greg's mini Square-1 & prisminx, but haven't assembled them yet. I have what my granddad told me were bolts rather than screws, and all the hardware shops tell me that M1 screws don't exist, only bolts. Is there a major difference? This puts me off buying DIY kits from shapeways.

Screws have pointed tips for tapping into wood, while bolts have flat ends for pre-existing holes. So most puzzles use bolts rather than screws, although everyone seems to wrongly call them screws when they mean bolts, probably including Shapeways. Your granddad is correct.

Screws also tend to have wider threads than bolts, to generate more driving force when tapping into solid wood.

Fantastic! I am going to be buying more shapeways puzzles soon then!

In short, screws are better designed to make new holes in soft material, while bolts are better designed to stay in place within pre-existing holes in hard material.

EDIT: Apparently there is no universally accepted distinction between a screw and a bolt, so my comments above reflect only my own personal views:

http://en.wikipedia.org/wiki/Screw#Diff ... _and_screw