Sorry,
I realised that I think I've bought the wrong reel seat.
ALPS do a fly tri fly seat and also a bigger spinning/carp rod one. The main difference is the physical size. The fly rod one has an internal diameter of 13mm, a length of 102.9mm and the code is R-TRI-AH12 and then the colour code of B, S or SCF.
Its designed for 6-8 weight rods, especially salt water.
The spinning rod version is 12, 14 or 16mm internal diameter, a length of 130mm or more (depends on the diameter) with a code TRI- and then the colour.
Hope that helps a little.