Park obw4 offset brake wrench 10 13mm park have answered the calls from both shop and home mechanics looking for a thin wrench to fit the centring flats pivot nuts and lock nuts on many popular brake callipers the new obw 4 wrench is the answer it has 10 11 12 and 13 mm openings and is specifically designed to fit the narrow flats found on some of these brakes that can make using standard wrenches difficult this tool is particularly useful when working on dual pivot and side pull brak