This set includes six plastic trays designed for storing 1/4", 3/8", and 1/2" drive sockets. The blue trays are suitable for metric deep and shallow sockets, labelled from 4.5 to 15mm (1/4"), 6 to 20mm (3/8"), and 10 to 27mm (1/2"). The black trays are for SAE sockets, labelled from 3/16" to 5/8" (1/4"), 1/4" to 1" (3/8"), and 3/8" to 1 1/4" (1/2"). Each tray is designed to keep your sockets organised and easily accessible.