12 transparent pieces Polyurethane anti-gravel film, permanent, 380µ These self-adhesive protectors for your road bike are based on 3M's top-of-the-range high-tech transparent film. Extra-thick (380 microns) and specially designed to absorb gravel and chain shocks, this film also protects against scratches and abrasion. The different-sized protectors are designed to protect the most exposed parts of your bike. You can place them under the downtube to protect against impacts, on the chainstay to protect against chain friction, and at various points of contact with the casings.