102mm Mullion
This multi-hollow section is 2mm narrower than the perimeter frame to match the 2mm internal frame radius. The centre web keeps the water on the outside of the weather line.

102mm Transom
The heavy, multi-hollow transom shown right is again 2mm narrower than the mullions to suit the 2mm mullion corner radius.
To soften the internal appearance, frame, mullion and transom have a 2mm internal corner radius.