The Park Tool CDG-2 Chainring Diameter Gauge, click to enlarge
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Item # CDG-2

(discontinued) / Tools / Crank & Bottom Bracket / Measurement

Chainring Diameter Gauge

The CDG-2 easily and accurately measures bolt circle diameter (BCD) in millimeters for a wide variety of four- and five-bolt chainring patterns. Made of anodized aluminum and permanently laser engraved, the tool centers itself in chainring holes, chainring bolts, or crank arm holes. The CDG-2 also includes a center-to-center distance scale and a handy reference chart listing additional mounting pattern measurements.

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CDG-2 Chainring Diameter Gauge