to those who have bought pop up caps from me.
a number of forum members have bought these caps from me.
the caps themselves are perfect.
but if anyone finds that they cannot screw them into the tank. the problem lies with the tanks thread.
so far it is only 2 tanks out of 25 plus that have this problem.
if you look at the thread in the tank, you will see one or two small lumps on the threads. we can only assume that they are there to maybe stop plastic caps from vibrating loose.
take a small punch and flatten the lump and the caps fit perfect.
chances are your tank will not have them, but this is to let you know there is a simple solution.