the MK4-3121 utilizes an internal spring-return mechanism that automatically retracts the actuator shaft upon loss of supply air

protecting the compressor motor from catastrophic failure

preventing the downtime and vibration issues common with universal aftermarket alternatives

or cracked porcelain insulators leading to a secondary short circuit

While both are 1/2-inch wide

Browning H 1 3/8 5/16 Bushing 320788-702 the MK4-3121 utilizes an internalThe Browning H 1 3 8 5 16 Bushing is a precision engineered split taper bushing designed for high torque mechanical power transmission in HVACR and industrial drive systems. Featuring a 1 3 8" bore diameter and a standard 5 16" x 5 32" keyseat, this component ensures a secure, concentric fit on the shaft, effectively eliminating the vibration and slippage common with straight bore pulleys. The Browning H series bushing utilizes a double split barrel