This is a 5610 Series single hung with an integral transom. The jamb is a continuous one-piece design. Unlike other window manufactures in which a transom is mounted on top of a single hung with an “H-mull”. This gives the window a more traditional look and also greatly improves leak issues that could be possible by a typical two-piece design. If ordering a 5640, all other items with the order should be ordered as 5610’s, such as Picture windows and stand along single hungs (i.e., no transoms on top).