i have looked at the downloadable content but i did not find it, can someone please help?
All dimensions can be found in Appendix A - Field Drawings, Specifications & BOM, which can be found on this page: https://vexforum.com/wiki/index.php/Gateway
Specifically the dimensions of the balls and barrels can be found on page 9 of the document titled VEX Gateway - Field Specs.20110404.pdf
The barrel is a cylinder that is 5" tall with a 6" diameter and has a 3" diameter cutout on both top and bottom which is 1.342" deep.
The ball is a sphere with a 6" diameter.