Abstract: An arbor apparatus for mounting an attachment to a rotary tool includes a mandrel with a drive stage insertable into a passage in a drive boss such that rotation of the mandrel rotates the boss. The boss has a polygonal drive head engageable with the drive opening of the attachment. One end of the mandrel has a locking plate that approaches the drive head when the mandrel is inserted into the boss. The locking plate is sized to pass through the drive opening while also partially extending radially beyond the edge of the drive head. With the mandrel inserted through the boss, the locking plate is passed through the drive opening of the attachment. With a gap being maintained between the locking plate and the drive head, the mandrel is manually rotated to allow the drive head to enter the drive opening, simultaneously causing portions of the locking plate to extend beyond the edges of the drive opening.