An apparatus for enabling the uniform application of a layer of a coating composition to a tubular substrate includes a shaft, and upper and lower circular rim members of equal diameter that are concentrically attached to the shaft. A pneumatically inflatable tube disposed on each circular rim member has an outer diameter that is variable with changes in its internal pressure. A first flexible cylindrical sheet in contact with the inflatable tubes has parallel edges that form a first slit sufficiently wide to permit movement of the first sheet in response to pressure variation in the tubes. A second flexible cylindrical sheet surrounding the first cylindrical sheet has parallel edges that form a second slit sufficiently wide to permit movement of the second sheet also in response to pressure variation. The second slit is laterally displaced from the first slit, and the second cylindrical sheet has a diameter nearly equal to the specified diameter of the substrate. Each of the tubes is inflatable to a pressure sufficient to provide the substrate with a smooth cylindrical outer surface for uniform application of a coating.