This is a dust port for the Excalibur EX21 scroll saw. It mounts to the underside of the table like the stock one and uses three 9mm by 3mm thick round magnets to hold the far end. The magnets are not needed though. Four M3 bolts and nuts hold the 2 pieces together.

My EX21 didn't come with mounting holes for a dust collector in the table so I had to drill and tap them myself. I tried to get the mounting holes close to stock from what I could find online but it may not be right.