These Drive Gears Are Made From High Silicon Copper Alloy ("Aluminum-Bronze") and Precision Machined. They Are Required When Using An 8620 Steel Billet Cam. Certain Special Crane Roller Camshafts Are Manufactured Using An "Iron Gear" Pressed Onto The Steel Billet Cam. These Special Cams Do Not Require An Aluminum Bronze Distributor Drive Gear. Refer To The Specific Camshaft Application Section Of Catalog. (Iron Gear Cams' Part Numbers Have An "Ig" Suffix At The End Of Their Part Numbers) Note: The "Shaft Diameter" Dimension Referred To Is The Portion Of The Distributor Shaft That The Gear Registers On. It May Be Necessary To Remove The Original Gear To Measure The Shaft Diameter Correctly.Pit Stop USA offers Crane Cams Bronze Distributor Gear - Aluminum, Bronze, .531" Diameter Shaft, Ford 221-302/ 351W 44990-1 at low everyday prices. Be sure to check out all of our products from Crane Cams including Crane Cams Bronze Distributor Gears,Distributor Gears.