Internal nipple wheels require a specialized tool that most spoke wrenches can't accommodate—the nipple sits inside the rim cavity, inaccessible to conventional wrenches that need to grip from the outside. Park Tool's SW-18 solves this with a socket-style design that drops into the rim and engages the nipple from above, letting you true wheels that would otherwise require rim tape removal or specialized shop equipment.

The 5.5mm hex fitting matches the internal nipples found on many carbon wheelsets and high-end aluminum rims where manufacturers route nipples internally for aerodynamics or rim bed simplicity. The forged steel construction handles the torque required for proper spoke tensioning without rounding, and the compact profile fits through standard access holes in the rim bed. A lanyard hole in the handle prevents dropped tools from disappearing into deep-section rims.

If you're maintaining wheels with internal nipples at home, this wrench eliminates the workaround of fishing around with hex keys or improvised tools. It's the same approach Park Tool takes with their external nipple wrenches—match the tool to the interface precisely, and wheel truing becomes straightforward rather than frustrating.