There are fine thread and coarse thread version of adapter, sounds like you are trying to fit a course thread into a fine .My female fittings screw on until they hit the sealing washer, remove the washer and they easily screw on further. The male adaptors, will not screw into the females more than a couple of turns. These are three different adaptors, all from my box of a motley collection of hozelock type fittings and adaptors.