Accessory Drill Chuck Attachment for Radial Arm Saws.
Chuck is a Jacobs brand. It has a 1/16" to 1/2" (1.5mm-13mm) bit capacity and fits the 1/2"-20 threaded accessory drive on most Craftsman, Ridgid, and Wards Radial Arm Saws.
Includes the chuck key.
The last two pictures show a typical accessory drive on the end of the saw motor.