Ultradyne UD Dynalock Arca Rail 6.15 Inch Black. By upgrading to the Arca Dynalock Rail you can enjoy the benefits of both Arca and Dynalock accessories on your firearm. The most popular enhancement is the ability to use the Orbit Ballhead with Dynalock all other Arca Clamp accessories are also compatible. Specifications for Ultradyne UD Dynalock Arca Rail: Manufacturer: Ultradyne Color: Black Finish: Hardcoat anodize Fabric/Material: 6061-T6 Aluminum Width: 1.5 in Condition: New Condition Quality: Excellent Condition Details: Other Last Chance: Yes Package Contents: Ultradyne UD Dynalock Arca Rail Ultradyne UD20081: UD Dynalock Arca Rail 6.15 Inch Black