When I had to replace the seals on a small Char-lynn hydraulic motor, it was held together with 12 point bolts. I think they were 5/16".
Has anyone used a 9mm, 11mm, 19mm 12pt socket on a 12pt fastener?
Head bolts on a Jeep is 1/2 or 13mm 12 pt. Can't remember for sure. Wheel bearings for Jeeps and late 90s Ram pickups were 12 point. Just changed a starter on a 2000 Ram Cummins that used 10mm 12 point bolts.
I've started to like 12 point sockets more, especially on larger bolts.

Has anyone used a 9mm, 11mm, 19mm 12pt socket on a 12pt fastener?

A PTO one? You don't see those too often.
13mm for the three bolts on my Wrangler's unit bearings.