Yankee Hill Machine 3-Lug HD 1-3/8in-24 tpi Aluminum/Stainless Steel. This fully enclosed assembly contains a mounting interface machined from 17-4 Stainless Steel-making it durable and capable of handling heavy use-including full auto. The HD 3-Lug Adapter is HUB compatible and uses the iconic HK tri-lug interface. This makes for a versatile adapter capable replacing any 1-3/8"-24 mount. The HD 3-Lug adapter can be swapped onto your R9 or Nitro N20 Sound Suppressors and can be used on some rifle calibers. This is the perfect upgrade if you are looking for a quick-attach mount with better longevity-especially on full auto platforms. Replaces any 1-3/8"-24 Mount. Aluminum and Stainless Steel Construction. Matte Black Finish Specifications for Yankee Hill Machine Heavy Duty 3-Lug Adapter: Manufacturer: Yankee Hill Machine Condition: New Package Contents: Yankee Hill Machine Heavy Duty 3-Lug Adapter Yankee Hill 2050 3-Lug HD 1-3/8''-24 Tpi Aluminum/Stainless Steel