FBS – Fiberglass Backed Supply and Return Air Diffusers from The Duct Shop are 24” x 24” and perfect for use in T-Bar ceilings for supply or return of Heat and Air Conditioning. FBS has a bright gloss white perforated face and a fiberglass back which is per-scored for 4” through 14” diameter collars. You will also need to purchase a Start Collar to connect your duct to the register
Installation Tip — First, you would cut the proper size hole into the fiberglass back of the diffuser using a sharp blade knife. Next, you would bend every other tab on a start collar out 90 degrees. Then you would insert the remaining straight tabs into the hole you just cut and then bend those tabs 90 degrees to the inside of the hole to hold the collar in place. We do recommend that you seal around the connection from the start collar to the diffuser with duct tape to prevent air leakage.