Canon EF 600mm f/4L IS III USM EF600mm f/4L IS III USM Instruction Manual - Page 22

Lens Cap Stowing the Lens Reverse the lens hood and slip it over the lens. Tripod mount Tighten the hood lock knob to fix the hood in Hood place securely with the lock knob in a line with the tripod mount. Attach the lens cap by slipping it on where the Draw strings hood lock knob is located as shown*. Use the hook and loop fastener and the strings to affix Hook and loop fastener the lens cap and prevent it from coming off easily. Lock knob * Fasten the hook and loop fastener around the lock knob. E-185C Lens cap ENG-21