Cover Plate fits 50 A receptacles.
Press Release Summary:

UL-listed, CSA-certified, square cover plate allows all 50 A Twist-Lock® receptacles to be installed in 4 in. square, 4 11/16 in., or 2-gang box. Made from stamped steel with concentric knockout holes, product includes extra mounting screws. Receptacles mount directly to cover with provided hardware.
Original Press Release:
50 Amp Receptacle Cover Plate
Hubbell Wiring Device-Kellems Introduces a 50A receptacle square cover plate as the newest member of the 50A Twist-Lock® product line. The new cover plate will allow all 50A Twist-Lock receptacles to be installed in a 4" square, 4 11/16" or 2-gang box. The cover plate is made from stamped steel with concentric knockout holes and includes extra mounting screws.
Features:
o Receptacles mount directly to cover.
o All needed hardware is provided.
o Fits 4" square, 4 11/16" and 2 gang boxes.
o UL Listed & CSA Certified
For more information go to hubbellnet.com/newsrelease
Hubbell Wiring Device-Kellems, Milford, CT