The diameters are designed to adapt specifically to the different materials used in the footwear sector. We are therefore with the diameter 1.75 which is the top of the range for use on very hard components such as beech: the spiked tip allows you to penetrate safely reducing the risk of creating breakage veins to zero. The 2.4 / 6 diameter is used on pre-drilled beech: it is the classic screw that we find in Dr. Scholl's shoes. The diameter 3 - 3.5 on the other hand is the non plus ultra on polyurethane beach shoes.
The aesthetics of this type of head has the classic shape of the boss with the addition of the fake washer, obtained however in a single piece instead of having the typical head-stem assembly: this guarantees a better seal of the upper and higher mechanical characteristics.