Bottle Jack Hydraulic Release Knob (Harbor Freight 12 ton)

This is a knob which goes over the release valve of the hydraulic jack which is on a Harbor Freight 12-ton press. It will probably fit other jacks as well.

I put a couple of holes in it in case you want to tie a string to it so it doesn't get lost, but mine is a tight press fit into the existing screw valve and it would be unlikely to fall off.