Some components, which are often optional accessories on sports bicycles, are standard features on utility bicycles to enhance their usefulness and comfort. Mudguards, or fenders, protect the cyclist and moving parts from spray when riding through wet areas and chainguards protect clothes from oil on the chain while preventing clothing from being caught between the chain and crankset teeth. Kick stands keep a bicycle upright when parked, while a bike lock will help prevent it from being stolen. Front-mounted baskets for carrying goods are often used. Luggage carriers and panniers mounted above the rear tire can be used to carry equipment or cargo. Parents sometimes add rear-mounted child seats and/or an auxiliary saddle fitted to the crossbar to transport children. Toe-clips and toestraps and clipless pedals help keep the foot locked in the proper position on the pedals, and enable the cyclist to pull as well as push the pedals—although not without their hazards, e.g. may lock foot in when needed to prevent a fall. Technical accessories include cyclocomputers for measuring speed, distance, heart rate, GPS data etc. Other accessories include lights, reflectors, security locks, mirror, water bottles and cages, and bell.[32] Bicycle helmets may help reduce injury in the event of a collision or accident, and a certified helmet is legally required for some riders in some jurisdictions. Helmets are classified as an accessory[32] or an item of clothing by others.[33] Many cyclists carry tool kits. These may include a tire patch kit (which, in turn, may contain any combination of a hand pump or CO2 Pump, tire levers, spare tubes, self-adhesive patches, or tube-patching material, an adhesive, a piece of sandpaper or a metal grater (for roughing the tube surfa

e to be patched),[34][35] and sometimes even a block of French chalk.), wrenches, hex keys, screwdrivers, and a chain tool. There are also cycling specific multi-tools that combine many of these implements into a single compact device. More specialized bicycle components may require more complex tools, including proprietary tools specific for a given manufacturer. Some bicycle parts, particularly hub-based gearing systems, are complex, and many cyclists prefer to leave maintenance and repairs to professional bicycle mechanics. In some areas it is possible to purchase road-side assistance from companies such as the Better World Club. Other cyclists maintain their own bicycles, perhaps as part of their enjoyment of the hobby of cycling or simply for economic reasons. A cyclist's ability to repair and maintain their own bicycle is also celebrated within the DIY movement. A luggage carrier, also commonly called a rack,[1][2][3] is a device attached to a bicycle to which cargo or panniers can be attached. This is popular with utility bicycles and touring bicycles. Bicycle luggage carriers may be mounted on the front or rear of a bicycle. The rear mount is more common. Bicycles may have eyelets, tapped with a standard thread, at the dropouts on the rear chainstays, and on the front fork blades. Mounting a bike rack is possible without these eyelets, but requires additional hardware. A style of rack clamps only to the seatpost, does not require eyelets or additional hardware, but has a limited capacity. Luggage carriers can be mounted on recumbents and on folding bicycles, but may require customization or additional hardware. Additionally, specialized or customized luggage carriers are often required on bicycles with (rear) disc brakes or full suspension.