The size of the socket available on the nut, for connection with a socket of the same size, in chestnut, wrench or air tool.

Allen

This concerns the size of the nose that the nut has, for Allen screw fastening.

Walnuts made of hardened metal, resistant to vibrations or impacts during work. They are suitable for demanding tasks and for use with air tools.

Walnut-shaped pieces with a narrow design, allowing for screwing screws and bolts into hard-to-reach areas.