These are replacement drive shafts to fit N Scale Bachamnn 4-4-0 American type Locomotives.
The larger Hex-Cup style for the older locomotives is available here.
The smaller Ball-Cup style for the newer locomotives is available here.
These parts are printed in the Shapeways FUD or FXD materials and it will require cleaning upon delivery, please see my FAQs for more information. To read more about these drive shafts please see this blog post.