I have bought the Ikelite Dome port 5503.15. But it has a very tight fit when installing it on the underwater housing. You have to press it a little bit to get it in place.
If I measure the diameter of the other ports I have, they are approximately 92mm while the small Ikelite Dome port 5503.15 is about 92.60mm.
Is it a manufacturing error or is it the thought/design that the small dome port 5503.15 has a very tight fit?
