Abstract: Roof curb structures include side shells made by cutting a series of transversely aligned V-shaped notches and straight slots along top and bottom edges of a continuous length of sheet metal strip material at spaced apart intervals corresponding to the length of each side of the side shells to be formed therefrom. Then the strip material is cut to length corresponding to the length of one, two or four sides of the side shells and the top and bottom edges are roll formed in opposite directions to form oppositely extending top and bottom flanges.

Abstract: A compact nestable air filter of generally rectangular form comprising a frame formed of an integral suitable cut and scored blank of paperboard, which, when assembled, comprises planar frame members engaging a substantially sheet-form filter element therebetween, and having flared frame members disposed at an angle of less than 180.degree. permitting a plurality of completed filters to nest within each other, thereby reducing the bulk of the plurality of filters. The end portions of the flared frame members may be connected together by several means, including glue flaps hingedly connected to one frame member and adhesively affixed to an adjacent member. In an improved embodiment the planar frame members on the bottom or downstream side of the filter are provided with an integral perforated cover sheet for retaining the filter element in place when subjected to an air current. The flared frame members are provided with edge panels interconnecting the upper and lower panels forming the frame members.

Abstract: A compact nestable air filter of generally rectangular form comprising a frame formed of an integral suitable cut and scored blank of paperboard, which, when assembled, comprises planar frame members engaging a substantially sheet-form filter element therebetween, and having flared frame members disposed at an angle of less than 180.degree. permitting a plurality of frames to nest within each other, thereby reducing the bulk of the plurality of filters. The portions of the flared frame members may be connected together by several means, including glue flaps hingedly connected to one frame member and adhesively affixed to an adjacent member. In an improved embodiment a portion of the planar frame members on the bottom or downstream side of the filter is provided with an integral perforated cover sheet for retaining the filter element in place when subjected to an air current.