The Ultradyne UD Spigot is a versatile and useful accessory for UD3, UD5, and UD7 Chassis systems, adding 3.25 inches of perfectly aligned Arca rail capacity. The M-LOK slots also make it possible to attach additional accessories including Picatinny rails. FeaturesDimensions: 4.75" x 1.5" x .448" (L x W x H)Arca Rail Length: 3.30"Materials: 6061 T6 Aluminum