What is the slot on the end hook?!?!!?

Suspension Fitting with Keyhole Slot for Use with Screw Hook hook slot slot whereby to retain the lever in place 2 A hame hook slot Another 1st from NSI! The Wind Ding hook replaces your overkill spreader bar with a smaller and smoother hook that will keep your board and pads ding

hooked slot 80mm Heavy duty L hooks pack of 4 Screw Hooks with Cross Slot With cross slot For machine assembly Galvanized steel Wall plugs Included