Westaflex/Uniflex have a range of adaptors manufactured from Plastic and Metal.
Uniflex/Westaflex adaptors suit most of the square diffusion that Westaflex manufacture as well as fitting some of the diffusers available from other manufacturers.
POLY
Poly Adaptor 'Snaps-On' to diffuser
No tools or fixing required
Made from High Impact Polystyrene
Positive lock duct tabs
Poly neck adaptors to suit Univents, CD 2000 and some aluminium diffusers