A R S 223 5.56 Extractor O-ring (Crane O-ring) 5 pack 5 Milspec MIL-R-83248C Chemical-Resistant Crane O-rings. 1 genuine ColtSP64026 upgraded M4Extr Spring Assembly (Milspec copper coated spring with black insert) This critical spring is designed for increased reliably and much longer life than standard springs. The Coltspring has been tested more than any other by far and it just works every time. The Coltspring is the only Milspec spring and gives extra power but still allows for full range of movement when compressed. Other extra power springs can limit the amount of movement on compression causing more problems than they fix. Made in USA. AR Specialties items are only available direct from AR Spec and not distributed through any other Amazon sellers.