Gear case
（重定向自Gearcase）
A gear case, also known as a chain case or chainguard, is an enclosure for the bicycle chain and sprocket assemblages commonly employed by utility bicycles. It serves to protect the cyclist from being soiled or trapped in the chain rings and tends to fully enclose the drive train. It may also contain an oil bath to keep the chain lubricated. Modern examples are usually moulded in plastic. Similar devices may be found in connection with chains used on larger vehicles and machinery.