They're made of thin steel and are nickel plated and heat treated for long use. Available in four popular sizes from 13mm to 18mm. Their small size makes them ideal to carry along for quick repairs.

13mm / 14mm - DCW-1 (this one)
15mm / 16mm - DCW-2
17mm / 18mm - DCW-3
13mm / 18mm - DCW-4 

Park Tool reference: DCW-1

About Park Tool USA :

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.

 

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