This is down to the aluminum spacer system that provides a solid core for the location of the nylon bobbin head.
Evotech Performance front spindle bobbins are retained by roll threaded stainless steel spindles for increased strength.
Evotech Performance spindle bobbin kits comprise of two nylon
bobbins, two anodized aluminum spacers, S/S spindle, nuts, washers and a
hollow spindle nut when required.