I found these in a lot of more modern coins and I know next to nothing about Roman coins. I know these are Probus but not much else. Can anyone tell me what they are. About 21-22MM and 3.8 - 4 gram. Also any recommendation of a guide book to roman coins would be appreciated.
I'd say check out Wildwinds under Probus or search on Vcoins for Probus antoninianus with the reverse legend (RESTITVT ORBIS).
Nice haul of Probus antoniniani - note the mark XXI in the exergue, you may want to research what it means a little more.