The stationary portion of a window that encloses either the glass (direct glaze) or the sash (operating or stationary) and consists of the following parts: HEAD JAMB: The top frame member. SILL: The bottom frame member. SUB-SILL: The supplemental member used under most awning and casement units as an additional sill with the primary purpose being to hold multiple units together at the sill. SIDE JAMB: Side or vertical frame members. JAMB EXTENSION: The addition onto the standard jamb to adapt a window unit to deeper wall thicknesses, in most cases will be factory applied unless specified otherwise. BRICK MOULD OR FLAT CASING: The exterior trim member applied to the side jambs and head jamb on wood units. Often used to secure the window to the wall opening. BLINDSTOP: The frame member on a doublehung window located between the jambs and the casing. The blind stop forms a rabbet that supports either a storm sash or screen.