This is captured single flat wound guide rod for your SAR 9. It will replace your factory guide rod that has some plastic components. This one is made from stainless steel, in swiss machine. Choose from the 17# or 20# spring and also choose from a black oxided retainer or a stainless retainer. The 20# is heavier and will help reduce muzzle flip but is a little harder to rack. The 17# is still a great option but much closer to your stock one. Whichever you choose, it is a great upgrade to this great gun!