This is a gear (part# 1347788) to replace the nylon gear that this oscillating spindle sander ships with that often breaks or arrives stripped.
I printed in PLA and was successful using it in the sander, however if I had any ABS material I probably would have used that instead.
Edit: Replaced original file with STL repaired with netfabb.
Edit 2: Much better product with ABS
I measured the provided nylon gear that shipped with the sander that arrived non-functional, and determined that the width needed to be a little bigger to decrease the gap between the gear and the spindle. It should fit on the rod perfectly without much force applied.