when putting on a dust cap wear latex gloves......... all you have to do is touch the sanded surface of the dust cap with oily/sweaty skin and it will come loose before gluing wipe the cone surface with 99% Isopropyl as well as the dustcap before it is sanded ...they will never come loose I also make a handle out of masking tape and stick it to the center of the dustcap so I have something to hold on to when I drop it into place