Yukon Gear & Axle
Steel Differential Cover For GM 8.0 Inch YP C5-GM8.0
Part # 4020091000
Differential drain plug. 1-inch diameter with 3/8 inch hex. Made from stainless steel with magnet to keep any metal shavings from going through your differential.
Details:

WARNING : This product can expose you to chemicals including arsenic, which is known to the State of California to cause cancer. For more information, go to www.P65Warnings.ca.gov