Ductboard collar

Claim 1

A fitting for connecting conduits to larger ducts, comprising: (a) a short length of full diameter sheet metal conduit of the size and shape of the conduit to be connected to the duct, having means at one end for communicating assembly with a conduit, and having a full cross-section at the opposite end, (b) externally directed bead means circumferentially formed in said sheet metal extending outwardly from the exterior of said short length conduit adjacent to and spaced from said full cross-section end, and said bead including a complete circumferential bearing surface for the wall of a duct, (c) the length of the full cross-section end beyond said bead means being essentially a distance equal to the thickness of a wall of a duct, and (d) a plurality of three or more spring clips means mounted on said short length of conduit at the full cross-section end arranged in general opposition to provide holding of said fitting to duct and arranged to compress permitting entry of the full cross-section end through a bore in the wall of a duct and to expand after such entry to bear against the interior of the wall of the duct to bias said bearing surface against the exterior of the wall of the duct around the bore therethrough, said spring means each including a flat spring section secured to the inside of said short length of conduit and extending toward and beyond said full cross-section opening and a 90° portion extending outwardly from said opposite end in position to contact the inside of a duct board and hold said fitting in an opening in a duct board when expanded.