The f1 stems come in two different sizes, 50-55mm and 40-45mm. Fits Rock Shox Boxxer & Fox 40 forks. Fits 31.8mm handle bars. Zero rise.
The f1.2 stem comes in one size the 50mm. Fits a 1 1/8" steerer tube fork. Adjustable rise - 0mm or 6mm. Knee friendly bolt clamp.