Plastic ball caster dimensions

I’m in the process of designing my next differentially steered, wheeled robot - two wheels in the front and a ball castor in the rear. I like the Plastic Ball Caster that is available at, but I need to know a few of its dimensions before I buy, to see if it will work with my design. A couple of dimensions are given on the website:

Overall length = 0.818"
Mounting shaft diameter = 0.390"

If I understand correctly, a 0.390" hole would be made into the underside body of the robot and the Plastic Ball Castor would be inserted into that hole. The most critical dimension that I need is the length of the Plastic Ball Castor portion that will sit outside of the body of the robot, the length from the underside of the body to the floor/ground. I need this dimension to make sure my robot would not tilted up or down.

Any other dimensions would also be very helpful.




The ball caster would stick out approximately 0.440" beyond the body of the robot.

The diameter of the unit is the largest at the middle flange, which is 0.550" across. The part of the housing that surrounds the ball is 0.475" at the widest point.