BAPL-4042 has a description of STEEL HEX NIPPLE JIC 5/16 TUBE X 3/8MPT

WARNING This product can expose you to chemicals, including Chromium which are known to the state of California to cause cancer and birth defects or other reproductive harm. For more information go to P65Warnings.ca.gov.  As alarming as the proposition 65 warnings may appear, you can rest assured that the products we sell remain the same as in the past. We encourage normal hygiene and discourage placing any of our products in your mouth, as they are not intended for human consumption.