4" inch, 4VP-WT, Pellet Wall Thimble. Type L pellet vent must be used for all through-the-wall installations, involving combustible construction. Maintains airspace clearance with combustibles and centers the pipe between the walls. Telescopic design can be used on standard walls 5" to 9" Inch thick. Rolled over male end eliminates sharp edges and internal spacing bead assures uniform insulating air space between pipe walls. From the Manufacturer 4" inch, 4VP-WT, Pellet Wall Thimble. Type L pellet vent must be used for all through-the-wall installations, involving combustible construction. Maintains airspace clearance with combustibles, and centers the pipe between the walls. Telescopic design can be used on standard walls 5" to 9" inches thick. Rolled over male end eliminates sharp edges, and internal spacing bead assures uniform insulating air space between pipe walls.