12" Clay Thimble 8" x 12" Catalog Chimney Items 12" Clay Thimble 8" x 12" Description Concrete Chimney Block | NYS Tek Spec 3.5 | Heat Stop Refractory Size: 8" x 12" Appx. Inside Dimension: 8 " Appx. Outside Dimension: 9 7/8" Spec Sheet Rates Please contact us for current pricing and availability. Request Availability