Among excellent makers of allen wrenches (think: Bondus, Allen, PBSwiss, Pedro’s, Park, Wihus, and others) only one has addressed engagement geometry like external socket wrenches have.
Historically, allen screws arose for embedded fasteners. The wrench inserts into a fastener rather than surrounding it. But the hexagonal interfaces have similar limits. In order to transmit maximum torque to a fastener without deformation drive shape was devised for external sockets, often known as “flank drive.” That name belongs to Snap-On, a socket drive pioneer but you’ll find such drive geometry everywhere today. Read more →