CTW stands for Curb to Wall. Provides a 4" wide nailer on the wall side and a CMF style flexible flange on the other. Smooth hinge area where nailers meet bellows, preventing a water dam. Nailing flanges conform to curb irregularities and angles without effort. No bent metal to force short lengths, excessive splices, and handling problems. Can be made up to 39" wide with 4" bellows or other standard bellow sizes. Can be supplied with pre-applied butyl tape on nailers. This size is for up to a 3" roof to wall structural opening.