Use to penetrate any interior or exterior combustible or non-combustible wall. This part is a thimble only and does not include any vent be sure to order enough vent to pass through the thimble. To use this thimble, the vent must be uninsulated for a minimum distance prior to passing through a combustible wall. A minimum distance of 18 in is required for appliance flue gas temperatures up to 400 deg F. A minimum distance of 6 ft is required for appliance flue gas temperatures of 400 to 480 deg F. The opening must be 6-1/2 in in Dia for both 3 or 4 in Dia Saf-T Vent® systems. The wall thimble is designed to adapt to any wall thickness from 3.5 to 6 in THK. If the wall is thicker than 6 in, the thimble may be extended using a piece of 6 in Dia snap lock or welded-seam galvanized pipe. The vent system may be terminated using any terminal listed for use with the appliance. The wall thimble may be painted to match the decor.