Started by the Pedalwise team from official manuals, support pages and repair videos

A cassette lockring tool is a splined socket that fits the lockring holding the cogs on a cassette rear hub. You turn it with a large wrench while a chain whip holds the cogs still.

What it's used for

You need it to replace a worn cassette, swap wheels or reach the hub. Park Tool's guide uses a lockring tool, a chain whip and a large adjustable wrench or 1 inch socket (Park Tool cassette guide).

What to look for

• Check whether you have a cassette or a freewheel first. A cassette slides onto a splined freehub and is held by a lockring, while a freewheel threads onto the hub. Park Tool notes many e-bikes may use the freewheel type, which needs a different tool (Park Tool).
• On hub motor bikes, Park Tool says freewheel removers may need extra-large center holes to clear the motor wiring (Park Tool e-bike tools).
• The right spline pattern. Shimano, SRAM and several other brands share one common tool, while Campagnolo needs its own (Park Tool).

Using it safely

• Turn counterclockwise to remove. Expect it to take real force and to make a loud ratcheting sound (Park Tool).
• Note the order of cogs and spacers as they come off and reinstall them the same way (Park Tool).
• Grease the lockring threads and tighten clockwise, no chain whip needed, to at least 40 Nm or the maker's value (Torque wrench) (Park Tool).
• Check rear derailleur adjustment afterward (Park Tool).

Guides that use it

• Check and replace a chain
• Adjust a rear derailleur

Sources

• Cassette removal and installation, Park Tool
• What tools do I need for my e-bike, Park Tool