Gear case

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. Similar devices may be found in connection with chains used on larger vehicles and machinery.

There are also a variety of smaller structures called chainguards which, rather than protecting the chain, serve only to protect the rider's clothes from being soiled or trapped in the chain rings.

Gallery

• 
  Fully enclosed chain on a European city bike
• 
  Partially enclosed chain on a European city bike
• 
  Huffy Flaming Stack chain guard
• 
  BMX bike with a chain guard bolted to the frame
• 
  Crankset with an integrated chainguard bolted to the outside of the largest chainring

References

• bicycle glossary entry for "Chain case" from Sheldon Brown's website
• Sheldon Brown's bicycle glossary entry for "Gear case"
• Sheldon Brown's bicycle glossary entry for "Chainguard"