Sunex makes good quality 4 pt. square plug sockets, bought one recently and it easily broke loose a very stubborn and damaged (by PO's) fill plug on my TR-6.
per Sunex:
Forged from the finest chrome molybdenum alloy steel-the best choice for strength and durability
Radius corner design-to extend the life of fasteners
The design drives the side of the fastener instead of the corner