The JerkStopper A Clamp from Tether Tools has polyvinyl-coated
jaws that open 1” to clamp to a round or flat object to provide an
anchor point and allow cable slack, which prevents damage resulting
from the tethered cable from being pulled out or tugged on while you're
shooting. A JerkStopper on the clamp handle, which can be rotated to
change the routing orientation, grips any cable with a diameter between
3.5mm and 8.5mm.