USED Salmon River Solutions SRS 4.25in Universal Picatinny Rail Black. It can be used with a standard sling stud and has an integrated flush cup for qd options. The 3.5'' version weighs .6 oz. And has bolt spacing of 1.25''-2.5''. The 4.25'' version weighs .65 oz. And has bolt spacing of 2.5''-3.25''. Specifications for Salmon River Solutions SRS Universal Picatinny Rail: Manufacturer: Salmon River Solutions Color: Black Finish: Anodized Fabric/Material: 7075 Aluminum Gun Rail: Picatinny Gun Type: Rifle Country of Origin: USA Features of Salmon River Solutions SRS Universal Picatinny Rail Picatinny QD Cup Sling Stud Package Contents: Salmon River Solutions SRS Universal Picatinny Rail M-Lok Fasteners 10-32 Fasteners Salmon River Solutions 1121: SRS 4.25in Universal Picatinny Rail Black