A wellhead system includes a bypass sleeve for temporarily isolating portions of a wellhead assembly from pressurized fracing fluid. The bypass sleeve may include a generally tubular body having a tool interface, a lock ring disposed at least partially around the body, and an anti-rotation device coupled to the body. The anti-rotation device includes a resilient member disposed in a cavity in the body, and an anti-rotation member biased away from the body by the resilient member. The anti-rotation member extends radially outward from the body.