A tool for securing a tap duct to an opening in a tap duct sized main duct having a base structure for extending transversely across and seating in supported relationship against the exterior open end of a tap duct flanged at the opposite end; an anvil structure movable so as to force the flanged end of said tap duct outwardly and toward the interior wall of a main duct; manually activated bending structure mounted on said base structure suitable for extending said anvil structure against the flanges of said tap duct outwardly and toward the interior wall of said main duct.