Material, surface finish:
Screw in tempered steel, quality class 10.9, black.
Ball in ball-bearing steel, hardened with natural finish.
Note:
Form A with full ball is used when a clean, polished pressure surface is required. Surfaces which are not plane and parallel can be firmly clamped or supported with form B with flattened ball because the movable ball can adapt itself up to 9°.
Fine thread enables extremely sensitive alignment of the ball pressure screws.