A firm grip.
Park Tool touts its 100-3D Professional Micro-Adjust Repair Stand Clamp as the best shop clamp it's created. In order to properly contextualize the enormity of that claim, it's worth considering that the blue-handle brand is the standard in virtually any LBS you step into. That makes this clamp the best of the best.
Compatible with a wide range of Park Tool repair stands, the clamp's aluminum main body, durable design, and replaceable jaw covers suit it to the demands of everyday shop use. It's also designed to be as adaptable as possible, complete with micro-adjustability for achieving the right grip on tubes measuring from 23 to 76mm and those with aerodynamic profiles. The narrow clamping arms give you clearance to grip short seatposts, and the Cam-actuated adjustment system keeps the operation running smoothly.
Compatible Park Tool repair stands include PRS-2, PRS-2 OS, PRS-2 OS-1, PRS-2 OS-2, PRS-2.2-1, PRS-2.2-2, PRS-3, PRS-3 OS, PRS-3 OS-1, PRS-3 OS-2, PRS-3.2-1, PRS-3.2-2, PRS-4, PRS-4 OS, PRS-4 OS-1, PRS-4OS-2, PRS-4W, and PRS-33.