The UNION GEAR 12Pitch 20 Teeth Bronze/Steel Worm Gear Set is a high-quality mechanical power transmission component designed for industrial automation and motion control systems. Made in the United States, this gear set features a 5:1 left-hand 20 teeth double lead design, perfect for various industrial applications. With a bore diameter of 0.6250 inches, this gear set is durable and reliable, making it a valuable addition to any machinery requiring efficient gear transmission.

Note: the Bore of the bronze gear is 1.025".  The part number of that gear is DB1600.  The worm is not marked.

Listing is for one set.  2 sets available.  I have another listing with a pair of identical sets except Right hand and mfd. by Boston Gear.