When we find a weak spot, we re-design, over build, and deliver. That's exactly what we have done with the factory Pro R & Turbo R Lower spring retainer cup. Built from 6065 billet, this RPM Retainer cup is nearly 6x stronger than the factory cast piece. We've retained the factory style, while increasing dimensions drastically throughout. The RPM spring cup is not only significantly stronger, but provides more surface area for the factory & aftermarket bottom springs to rest on. These work on factory & RPM HD shock tuning forks. Pair with our RPM Front Tuning Forks for the ultimate bullet proof front end! Sold as a set. Replaces OEM # 5634675 .