There were a few requests in another topic to purchase this jig. It is a 3D-printed block that assists in reassembly of the USAT locomotive axles by centering the gear and assuring the correct back-to-back wheel measurement (40 mm). There are two versions: 2-axle and 3-axle.
As with anything I design, the files are open source, and you’re welcome to print your own. Here are the files:
$20, including shipping
To order, send the money via PayPal Friends and Family to eric at southroad.net
Be sure to specify 2-axle or 3-axle.
I can also accept Apple Pay or Google Pay on request.
EDIT: 3-axle jig now tested