Stud 5 passes freely through the hole in right-hand shoe 2 and is screwed tightly into left-hand shoe 2. When nut 1 is tightened, shoes 2 clamp round workpiece 3, forcing it upward into upper part a of the base member. Springs 4 serve to spread shoes 2, returning them to their initial position, when nut 1 is released.
$210$SL,GC$