Here is an enigmatic denomination. The coin is only 10 mm in diameter and 1.18 grams, with a bust of Hadrian right, with no legend and, on the reverse, SC in a wreath.
There is some question about whether it should be classified as Roman imperial or provincial. It is in Sear, volume 2, 3705 given to the Rome mint. It is RIC 629b of Rome. However, BMC says "very probably not of Roman mintage--possibly Antioch" (because of the "SC" types so common at Antioch.) Both call the denomination as "uncia", but without conviction. They note it might be one third of a quadrans, but it is a bit too heavy for that.
Lindgren III gives it to Antioch, as does BMC Greek Syria, page 185, plate XXII.10. Butcher, "Coinage in Roman Syria" is the latest word on the subject and he has it as Antioch, #240-248 (with different letters, missing or A though theta, in the wreath) . The letter on this one might be an A.

10 mm is really small! Scholars now seem to think it is provincial, as opposed to imperial. In that case, instead of being the smallest imperial denomination until very late Rome, it is instead the smallest provincial denomination. Butcher says it might be a "1/12 unit" where the unit is the largest denomination of the time.