Leupold Mark AR bases are made to be durable and dependable with 5 mounting bolts and 3 lugs to integrate with your top rail they will mount solidly and stay where you put them. They are precision machined from aircraft-grade aluminum and will provide the strength you expect without adding excess weight. Leupold & Stevens, Inc. is an American, family-owned, fifth-generation company that has been designing, machining, and assembling precision optical instruments and other products for 110 years. Founded in 1907, Leupold's success has been built on their commitment to the customer's absolute satisfaction, and their ability to build the best optics and accessories in the shooting sports market.