16mm U groove combined with 14-18mm C groove.
Alu-wood profile is more and more popular now, because of its strength of alu. profile and decorative effect of wood cover. It is not proper to use simply the normal PVC & Wood window fittings, as it will cause severe danger to the hinge fixed, as well as damage to the wood surface. HOPO ATT90 combine fittings of 16mm U groove and 14-18mm C groove, directly fixed to the Alu. profile with no screws.