What I use on my head cement jars, the square ones with the metal screw-on cap, is replace the metal cap with a Heinz ketchup cap. It is the one with the flip-up top and the small hole to squeeze out the ketchup. It will thread on the jar perfectly and you only have to flip up the cap and insert your bodkin through the small hole that is already there. Depending on the diameter of your bodkin, you may need to enlarge the small hole. I use Sally Hansons and just add to the bottle as needed. It seems to seal pretty good for me. Just a thought......