With compact size of head portion, convenient at narrow space.
With surface contact(*), suitable for final tightening

　
* From linear to surface contact, avoid concentration of stress and reduce damage of the corner of bolt/nut.Then, achieve firm tightening.
Easy to grip, Hard to bent owing to its cross section shape!
For larger size (over 21, except 27), optimized with longer haft for easy to apply torque
Improved visibility with bigger size display
With satin finish, hard to slip in case of oil-stained
With Spanner, temporary tightening & with Offset wrench, final tightening