8" Type B Firestop Spacer Square 8GVFS This firestop spacer can help provide additional clearance from your venting to combustibles ensuring better fire protection. Use at every ceiling level where Square Firestop Support is not used. For Category 1 gas appliances 1" clearance to combustibles Easy-fit twist-lock design with no fitting hassles 0.012" aluminum inner 0.018" galvanized outer .010†Double-wall aluminum flex inner wall (two-ply .005â€) .018†galvalume outer wall with twist-lock connections.