Update, Version 3: Added a Ball holding Collar so you can use less Bearing Balls. But keep in Mind: no error checking! You have to find your own fitting Parameters ;-)

Update, Version 2: Updated the Bearing. Now you can preview the Bearing Balls in 3D.

This is the parametrical Bearing ( https://www.thingiverse.com/thing:1799757 ) for FreeCAD. It uses Spreadsheets so you easily can customize it to your needs.

You can use 6mm Airsoft Pellets for plastic only Bearings or any size of steel bearing balls (i use 4,5mm steel bearing balls)

Usage:
Load the File in FreeCAD (i use 0.16) and double-click the "Params" Spreadsheet Symbol.
Then you can arrange the Preview and the Spreadsheet Windows in the "Windows" Menu like shown in the Screenshots.

Now you can adjust the Values in the Spreadsheet and watch the Bearing change in the preview Window. There are some calculated Values to help you optimizing the Bearing:

Orbit in the middle: If you copy this Value to Field B8, the BBs will be placed in the middle between inner and outer Radius.

Best Orbit: Tries to calculate the best Orbit according to the number of used Bearing Balls (Field: B9). Copy this Value to Field B8.

Ring Spacing: The amount of space between the inner and outer Ring. Default is half of the Ball Diameter.

Be careful when changing the Values because there is no Error checking!
Also you have to find out the right Tolerance setting ("Printer tolerance") for your Printer by trying...
Also only Export the Object "Bearing, complete"! The "BB shapes Pattern" and "Ball Array" Objects are only for previewing optimizing the Bearing Values!