Probably buck rivets which are a solid rivet smashed into place with either an air hammer or press. They fill the hole completely with rivet expanding inside it.The pulley is riveted with some weird rivets. I took a die grinder to them and managed to separate the pulley and expose the bearing but no matter how hard I try I cannot get the "rivets" out of the hub portion. I have tried grinding them off flush, and pounding the living s^&t out of them and they will not loosen up or come out. I guess I will have to bite the bullet. The machine is a later model so I suspect it could be from late mid to late 90's so perhaps anywhere from 20 to 25 years old. I guess if it lasted this long if I go through all this it should last another 10 years anyway. **** at my age I don't even buy green bananas anymore <img src="http://www.mytractorforum.com/images/smilies/biggrin.gif" border="0" alt="" title="Big Grin" class="inlineimg" /> so I am thinking with a little regular care it should be fine for a long time to come. **** it lived it's whole life up until last summer when I bought it mowing close to 2 acres. I only have a half acre so it should be fine. I just hate parting with the coin is all.
Once I have it all done I will flush the cooling system, replace the coolant with fresh, I touched up a couple little rust spots on the deck and sharpened the blades, installed a new belt as well so all should be well there.
You have to punch them out with an air hammer or drill them out if thats what they are.