These are replacement cheek pads for the S1 Retro Lifer Helmet.  All Retro Lifer Helmets come standard with 20mm removable cheek pads. If you own an S1 Retro Lifer Helmet and you feel that the standard 20mm cheek pads are too thick and you would like some more room around your face then the 15mm cheek pads are what you need. If the 20mm cheek pads are to thin then the 25mm cheek pads will tighten the Retro Lifer on your cheeks. 
 There are 2 generations of the Retro Lifer with different cheek pad mounting. See photos