The Astro Tool 94404 Magnetic Spark Plug Universal Extension Socket Set incorporates a full magnetic ring for a more securely retained spark plug compared to other magnetic and bushing style spark plug sockets. The universal swivel design increases access and articulates with little resistance and sockets feature minimal outside diameters for tight cylinder head clearances. All sizes are 6-point 3/8" drive and display permanently engraved sizes: 9/16" x 6", 5/8" (16mm) x 6", 5/8" (16mm) x 10", and 13/16" x 6". For use with most import and domestic vehicles.