N-PowerFit Drive- Increased strength and reduces rounding or fastener damage by distributing stress through a gentle arc in the bore by enlarging the contact surface. Designed for maximum strength with minimal wall thickness made possible by tough materials, advanced processing technology, and optimal heat treatment. Optimal fastener fit- industry leading tolerances Set Includes: 1/4″ Sockets, B2-3/16, B2-7/32, B2-1/4, B2-9/32, B2-5/16, B2-11/32, B2-3/8, B2-7/16, B2-1/2, B2-9/16, EHB215-Socket Rail for 15 Sockets .