This is often credited as being the first modern rear derailleur.

Notice the two small screws on the body of the rear derailleur.

While this was once a common design for rear derailleurs, it is relatively uncommon today.

No, you must use the dedicated rear derailleur with the medium length cage.

Given the rear derailleur hanger, it would appear to have been used as a test bed for a number of different items.

Although variations exist, as noted below, most rear derailleurs have several components in common.

Full 105 bike, with the exception of an Ultegra rear derailleur.

OK, some upgrades, the seatpost and rear derailleur are fairly recent.

He was a pre-race favorite, but had to withdraw from the race with a broken rear derailleur.

The chain has pulled the rear derailleur pulleys apart.

Eliminating a rear derailleur makes bagging a bit easier.

And then my rear derailleur slipped a gear.

This requires a sprung chain tensioner, similar to a rear derailleur, to be used.

The distance between the upper and lower pulleys of a rear derailleur is known as the cage length.

Derailleur adjustments Keep both front and rear derailleurs adjusted.

The rear derailleur has shift times similar to mechanical systems and a break-away system to protect it in case of a crash.

A cogset works with a rear derailleur to provide multiple gear ratios to the rider.

Luckily Jason had given me a chance to catch up, by having one of the jockey wheels from his rear derailleur fall out.

Typical cross country mountain bikes with three front chainrings will use a long cage rear derailleur.

In the midst of trying to follow John and power pedalling up the hill, my rear derailleur suddenly made a loud snap.

All Rowbikes have a rear derailleur, even single speeds, due to the need to keep proper tension in the chain.

Economy Rear Derailleur This one is made of steel.

Meeting both these requirements is only possible if the rear derailleur is compatible with the gear range being used on the bike.

You need a rear derailleur with a longer cage than that XX (for a double) has.

As with the rear derailleur, the front derailleur has a cage through which the chain passes.