Watch List notes:

Probo (276-282), Aureliano, Pannonia.; Bi 4,98 g; IMP C MAR AVR PROBVS AVG, radiate bust right; in rev. CLEMENTIA TEMP, Probus and Jupiter, B in field, XXI in exergue.
Extremely fine.

Aurelian refermed the coinage fixing a five percent of silver in its coins, represented by XXI, the twentieth part was indeed the content of precious metal.
RIC 644
Bella y bien conservada. EBC