This is a replacement set of 4 axles and 2 drive gears for a HO Scale Bachmann 4-8-4 Northern, First Version/generation. Only 3 regular axles are required per locomotive as the 4th axle has the gear between the wheels. An extra axle has the square drive used on some locos for sound/smoke synchronization. 2 gears have been provided, one twice as thick as the original and one three times as thick. The thicker gear will be stronger as the teeth are wider but it may limit the sideways movement of the rear axle, which may cause an issue on a tight radius. The thinner gear allows the movement.
Please note it's important to clean the inside of the axles and gear before inserting the wheel peg. Leaving any 3D print residue inside may cause the new parts to split when pushed onto the wheels. I recommend reaming the hole with a 2mm (0.078") drill.
These are designed to replace the original split axles.
These parts have been designed for Smooth Fine Detail materials.
For more information please see my blog - www.jamestrainparts.wordpress.com