A 3d model for a swiveling offset caster. What is different is that it is highly parameterized so you can use this Fusion model to create any number of versions. In particular, you can pick a wheel size and the overall hight of the caster. It uses two ball bearings so it is extremely smooth. 

There are four separate parts that you need to print:

1. The fork
2. The wheel (which needs one ball bearing)
3. The axle
4. The Plate (which attaches to the bottom of the vehicle)

The ballbearings are F623-2RS. I got them on amazon