Guzzi part number 1766-0253. Imported from Italy, a seemingly fine copy of the round-reservoir front brake master cylinder used on Guzzi machines from the mid-70s through early 80s, and other Italian makes with single front disc. Pistons diameter should be 12mm or so, to suit the linked brake systems or ONE disc applications.

Exterior paint finish could be a little better, but genuine Brembo lever seems to fit well, piston moves smoothly as it should.