Crank bolts and bottom brackets require specific wrench flats that adjustable wrenches can't reliably grip. The Park Tool HCW-4 combines the two most common sizes on a single stamped steel tool: a 36mm wrench for adjustable cup bottom brackets and a 15mm wrench for crank arm mounting bolts. Both ends feature the thin profile necessary to fit into the recessed areas where these fasteners live.

The 36mm end fits adjustable-side bottom bracket cups on BSA-threaded frames—the loose cup you turn to set bearing preload before locking everything down. That same 36mm flat also works on some older fixed cups, though many of those require a spanner wrench instead. The 15mm end handles the bolts that secure square taper and similar crank arms to the spindle. These aren't the same as pedal flats, which also happen to be 15mm. Crank bolts sit deeper in the arm and need a thinner wrench to clear the surrounding material.

Stamped steel construction keeps the tool light enough to justify wall-hanging storage and affordable enough that home mechanics don't need to borrow from a shop. The length provides adequate leverage for proper torque on both fasteners without encouraging the kind of force that strips threads or cracks cups. Park Tool heat-treats the steel for durability at the contact surfaces where cheap wrenches tend to spread and round off.... Read More