Xiaomi BHR5722GL The foils themselves have a certain thickness, which can cause shorter stubble to be missed. To solve this problem, Mi Electric Shaver S700 Replacement Heads are equipped with a thin 0.08 mm secondary foil blade mounted on top of the outer track of the primary blade. The secondary blade lifts the hairs before the main blade quickly cuts them off, resulting in a cleaner and more thorough shave.