I received an order of train wheels and frames but they didn't come with the axles.
Here is how to make your own metal axles.
1. You'll need 2mm diameter metal rods. You can find them at local hobby stores or online.
2. Cut the rods to 40mm in length. You can use an original LEGO metal axle for reference.
3. Smooth out the ends with a metal file or bench grinder.
4. Optional: Buffer them to a shine.
It was pretty wild when the cutting disc shattered and flew everywhere. Wearing eye protection is a good idea.