these grommets are to be used with car audio 1/0 cable, pictured is D4S 1/0
 
when installing these i use a 1 inch hole saw and then a file to get a tight fitment, if you use a 1 1/4 inch hole saw the waterproof gasket may not seat correctly
 
ALWAYS CHECK UNDERNEATH / ABOVE WHERE YOU ARE DRILLING, you dont want to drill through a wire, or worse a fuel line :)