Hubbell HBL9367 Heavy Duty NEMA 6-50R Welder outlet (top of the line Hubbell, not the less expensive light-duty Leviton or others that melt). Was installed but not used as I changed to 4 prong Hubbell 14-50R. Excellent condition. $25
SIGMA ENGINEERED SOLUTIONS 14321 Weatherproof Outdoor 20/50 Amp Outlet Cover, Gray, Metal, 2-Gang, designed for a 2.125-inch diameter outlet mounted in a 2-gang weatherproof box. $10/ea (2 available)