This is a telescopic plastic cavity wall sleeve.
The cavity sleeve here is actually metric and is designed for use with a pair of external Windsor, metric cast iron air bricks item WIN6 . It can be bought as a package with the air bricks (WIN6) and cavity wall sleeve (CAVHEXT6) as item number CAV6 with either a bare metal or painted black air bricks. The sleeve is extendable from 230mm to 384mm. It can be reduced in length by removing the adjustable sleeve and sawing or cutting the plastic to length and there are reinforcing ribs along the plastic at varoius lengths to make this easier.
The cavity wall sleeve can be extended by adding another CAVHEXT6 so the sleeves can be used in walls thicker than 384mm.
For interiors, the 10×7 inch flange is ideally suited for use combined with a 10×7 inch flat grille such as the DAISY grille item DAY107, mesh can be used internally to keep out bugs etc. The baffles within the CAVHEXT6 form a rigid structure that also reduces back draughts and reduces the free area to 13,000mm2. This means the CAVHEXT6 can be used with all our 9×6 inch cast iron air bricks without reducing the free area with one exception. When used with the MAX6 air brick, the maximum free area from this air brick will be 13,000mm2 and not 18,000mm2