Cassette Lockring or Freewheel Tool - FR-5 - from Park Tool USA

Also fits Shimano disc brake lockrings.

The FR-5 has 12 splines that are approximately 23.4mm across.

Note: Always use a quick release skewer to hold the tool in place and snug to cogs when loosening.

For solid axles, use the axle nut

Note: You will also need a chain whip tool to hold the cog in place.

Weight: 61.6g (2.2oz) 

Park Tool Reference: FR-5

About Park Tool :

Park Tool has been manufacturing bicycle specific tools since 1963.

Based in St. Paul, Minnesota, USA, Park Tool is the world's largest bicycle tool manufacturer.

A long-term dedication to quality, innovation, and customer service has made Park Tool the first choice of professional and home bicycle mechanics around the world.

Just visit your local bike shop - chances are that they will be using Park Tool tools for bike service / repair.

Related tags: Freewheel Lockring Park Tool