Selkirk 6" to 8" Insulated Wall Thimble (Double Wall Stove Pipe - DSP)Selkirk 6" 7" 8" Insulated Wall Thimble This wall thimble is used for installation through a combustible wall to a masonry chimney. It is used to connect a single or double wall stove pipe to an existing masonry chimney or a relined masonry chimney with a stainless steel liner. DSP Double Wall Stove PipeClose clearance, double wall connector used to connect a gas, liquid or solid fuel burning appliance to a chimney. DSP's better insulating value means