A magnetically driven centrifugal pump has a pump case, an open vane impeller in the pump case, a stuffing box including a stuffing box outer being fixed relative to the pump case and a stuffing box inner threadedly engaged with the stuffing box outer, and a rotor axially fixed and rotatably mounted in the stuffing box inner. Bushings are arranged between the rotor and the stuffing box inner. A drive is fixed relative to the pump case and includes a drive output extending into the rotor. There is a magnetic coupling between the rotor and the drive and a canister fixed to the stuffing box and extending through the magnetic coupling to isolate the rotor from the drive. A rub ring closes the end of the stuffing box inner and constrains the drive output from damaging the canister under catastrophic bearing failure.