These aluminum barrel nuts slide into ?" (9.5mm) awning rails mounted along the top rim of many campers, trailers, and RVs. Stainless steel eye bolts are held in place with neoprene-backed stainless steel washers, allowing you to securely anchor your MoonShade to your pre-installed awning rail. Includes 2. Have a 1/2" sized awning rail? Check out our Basecamp Rail Anchors . Product Specs Materials Aluminum Cylindrical Nut 0.375in (9.525mm) diameter by 1in (25.4mm) length Ring Bolt 1.00in (25.4mm) Length Ring Bolt inner diameter 0.5in (12.7mm) Dimensions 9.5mm