Abstract: A coupling ring for joining circular sheet metal ducts has oppositely opening grooves for receiving meeting ends of the ducts, and is diametrically adjustable to accommodate variations in the duct diameters.

Abstract: A machine for coiling a sheet metal strip having a pair of lateral flanges joined by a channel shaped rib with oppositely opening lateral grooves where the rib is on the outside of the coil, includes a pair of cooperating fluting rolls between which the strip is fed to flute the flanges, one roll being circumferentially grooved to receive the rib of the strip, and a wedge shaped coiling shoe is positioned to receive the strip from the rolls. The shoe has three strip coiling ramps, two of which bear against the flanges and embrace the rib, and the third bears against the top of the rib. These ramps are positioned to deflect the strip into a coiled configuration. A pair of ears on the coiling shoe enters the oppositely opening lateral grooves and cooperatively with the fluting of the flanges prevents collapse or distortion of the grooves.

Abstract: A coupling ring for circular ducts is formed of a single piece of sheet metal and has oppositely extending flanges connected together by an annular channel-shaped rib which cooperatively with the flanges defines oppositely opening grooves containing sealant. The relative dimensions of the grooves is such that a hydraulic lock is avoided at the time the coupling ring is telescoped onto the ducts. Proper sealing can be visually determined by inspection.

Abstract: An access door for an air conditioning duct or the like has a circular frame intended to be rotated into a circular opening in the duct wall. The frame has an inwardly extending circular shoulder against which abuts a removable circular door held in place by latch means engaging within a circular groove formed in the frame.