Product Description 17-4PH Heat Treated Material; Melonite QPQ Finish; 1.375"-24 Mounting Threads; .45 Cal Bore; Weight: 1.7 oz YANKEE HILL MACHINE CO HUB Direct Thread Mount System 5/8"-32 (YHM-2189-32) at GritrSports $61.86 Buy Now Check Price on Amazon Check Price on eBay