Per strict Keirin regulations,"The distance from the center of the frame to the center of the chainring should be 42mm +/- 2 mm."

This product responds to a request to manufacture a gauge that instantly measures this inspection standard.

To use, place the V-groove of the gauge on the seat tube, and use the center line of the groove with a width of 42 mm to the center line of the protrusion and the thick line extending 2 mm to the left and right from the center line of the protrusion, and confirm the standard of 42 mm +/- 2 mm. increase. If the cutting edge of the chain ring fits in the thick line of the protrusion, it can be judged that the inspection standard is satisfied.

Laser-cut from 1.5mm stainless steel, any burrs left behind on the product after the cutting process are removed by hand, leaving smooth edges to improve safety and workability. When measuring, care should still be taken to prevent scratches to your seat tube when it comes in contact with the cross section of the V groove.

Please note that this gauge was made for inspecting chainline on NJS frames with a 68mm bottom bracket shell. If your frame has a wider shell, the measurement may not be 100% accurate.