Product Description Harris Engineering 6A: The American Rail Adapter Stud HB6A is for for American size rails, 5/16\" across the rail slot. Harris 6A HB6A American Rail Adapter Stud 5/16\" Metal at Classic Firearms Browse all Classic Firearms deals $13.34 In Stock at Classic Firearms Buy Now at Classic Firearms Secure checkout Easy returns or compare prices Amazon eBay Product Details Brand Harris Engineering MPN 6A Accessories Harris Engineering