1) Bicycle part 
A gear case, also known as a chain case, is an enclosure for the bicycle chain and sprocket assemblages commonly employed by utility bicycles. It serves to protect the chain from mud and dirt 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. Sim...
a protective casing providing a reservoir of oil or grease for the gearing