Slotted chainring nuts sit on the backside of the crank spider, sandwiched into a space so tight that standard wrenches and pliers can't reach them. When you try to tighten or loosen a chainring bolt from the front with a 5mm hex wrench, the nut on the back just spins — and that's where Park Tool's CNW-2 Chainring Nut Wrench comes in. The tool's thin steel profile slides into the narrow gap between the nut and the spider, and engagement tips drop into the nut's slots to hold it stationary while you drive the bolt from the opposite side.

The CNW-2 is double-ended, with 2 different tip widths to accommodate the range of slotted chainring nuts you'll encounter across road, mountain, and touring cranksets. One end has tips nominally 2.7mm wide, and the other has tips at 3.8mm — both ends share a 12mm outer width. The blade thickness is 1.35mm, thin enough to fit the tight clearances between nut and spider without fouling on the chainring or crankarm. That includes compatibility with Campagnolo chainring nuts, which use a different slot profile than most Shimano and SRAM equivalents.

If you're swapping chainrings, replacing worn bolts, or building up a crankset from scratch, the CNW-2 is the dedicated tool for the job. Keep in mind that this tool applies to cranksets using traditional bolt-circle chainring mounting with slotted nuts — if your setup uses a direct-mount chainring, hidden bolts, or a proprietary fastener system, those don't use slotted nuts and the CNW-2 won't apply. For everything else, it's the tool that turns a frustrating, knuckle-scraping task into a quick one.