C.R. LAURENCE B640 CRL 1" Nylon Ball Bearing Sliding Screen Door Spring Tension Roller . One of the most popular rollers made, this CRL Spring Tension Roller is used by several patio door manufacturers. The steel spring is coiled in a "S" configuration, and is made of heat treated, high tension steel spring; used by several patio door manufacturers. The 1" (25.4 mm) nylon ball bearing wheel has a 1/4" (6.4 mm) center groove. Two roller assemblies with installation screws per package..