Precision Reflex Gen I Replacement Post for Gas Block Base Black. This post will work on PRI's 750 and 625 diameter front sight gas block bases. The post comes full assembled all you need to do is remove old post by tapping pin out of the bottom of the base from the front to back. Be careful to catch the tension spring in the pivot pin housing. Specifications for Precision Reflex Gen I Replacement Post f/Gas Blocks Base: Manufacturer: Precision Reflex Color: Black Fabric/Material: Aluminum Model Generation: 1 Package Contents: Precision Reflex Gen I Replacement Post f/Gas Blocks Base Precision Reflex 05-G1-Post: Gen I Replacement Post for Gas Block Base Black