New Old Stock 16:21 gear set 29513 A1 commonly called Conversion gears since they were part of one of the three kits Mercury sold to improved the preformance of the Mark 20H engine. We have three sets of OEM gears and two sets of what look like reproduction gears since they are coated in black phosphate. The discoloration appearing in the pictures is a rust preventive coating that rinses off in a parts washer and was used as the name implies to prevent the gears from rusting while on the shelf.