Okay, say you have a cylinder with a circumference of exactly 2.00000000000000 inches (as exact as possible) and you also have a round hole also with a circumference of exactly 2.00000000000000 inches. Assume both are made of the same very hard material… steel or something that doesn’t compress easily (not marshmallow). Assume both the cylinder and the hole are perfectly round and measured as exactly as possible.
Now lets put the cylinder into the hole. If the cylinder were slightly larger than the hole obviously it would have some friction (increasing up to the point it didn’t fit at all) and if it were smaller than the hole obviously it would fit in without any friction. But what if the sizes are exactly the same, or as exact as humanly possible? (If you just cut the cylinder out of some material to make the hole at the same time, there would presumably be some lost material due to kerf making the cylinder at least marginally smaller than the hole).
If you put the cylinder into the hole, would the fit be tight? Would it slide right into place without any friction at all? Would there be a small amount of friction? If so, does the amount of friction rise or fall with the exactness of the two sizes?
I do think of ice frozen into a glass - it’s the same size - but due to the expansion of water I’d assume that is the reason it holds itself in so well… at least until it melts a bit and then slides right out (due in part to lubrication).