A-B1166X44MA-AI SPRING-TORSION 20 RBOne New Aftermarket Replacement Torsion Spring (20 RB) for Murray Lawn Mowers This torsion spring (part type: Spring Torsion 20 RB) is a direct aftermarket replacement for Murray walk behind lawn mowers. The spring supports the rear discharge door assembly, holding the grass catcher panel firmly against the mower deck opening where cut grass exits. A broken or missing torsion spring allows the rear door and grass bag to lose tension and fall away from