Amazon.com Product Description
This Jet Table Insert is a useful addition to your JET oscillating spindle sander (#708404), giving you a tabletop fill for supporting your work-piece and keeping it flush with the sanding sleeve. Attachment and removal is easy, and the single-nipple drop-in device allows you to consistently install the insert in the same position every time. This table insert measures 3 inches and is intended for use with a 3-inch rubber drum.
From the Manufacturer
3" Table Insert for use with 3" Rubber Drum