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Expert Answer
This product is compatible with all small pin receivers, which is pretty much everything except some Colts from a specific time period.
Colt is the only AR-15 rifle manufacturer to use both small and large diameter pins in their trigger groups. Most Colt AR-15 rifles manufactured before 1991 and after fall 2009 are likely small pins, while rifles manufactured between 1991 and the fall of 2009 are likely large pins.
If you're unsure, measure the front takedown pin hole. If it’s .25″, then you have a small pin receiver. .315″ is the large pin receiver.
Mark H.