CALIFORNIA WARNING: This product can expose you to chemicals, including lead and DEHP, which are known to the State of California to cause cancer and birth defects, or other reproductive harm. For more information, go to https://www.p65warnings.ca.gov.
1" diameter carbon steel ball is used on a few electromechanical pinball machines from the 1960's and on Bally TRUCKSTOP to improve ramp shot playability.
The standard pinball used for all recent equipment is 1-1/16" diameter.
Reference:
PB1