13.5MM Thick and 2.7" in length. 11/0 Swivel hook for 3/8 sidechain. Swivel Hooks are made from case hardened steel and are not to be pressed closed. It can be tricky to install these hooks at first because of the very close tolerance fit that helps retain the cross chain. Feed hook through the side chain, angle the hook to get smallest opening against side chain, place cross chain between link on side chain, then swivel hook to capture cross chain.