This page links to templates to identify chainring bolt-circle diameters directly. You print out a template and lay the chainring down on it.
Use this page in connection with our bolt-circle diameter cribsheet, which identifies the major brands and models associated with each bolt-circle pattern.
Below are thumbnail images with clickable links to full-sized PDF templates which you can print out. These templates cover bolt patterns for all bolt-on chainring models, old and new, of which we know. We are not absolutely sure of dimensions for some chainrings with uneven bolt hole spacing. If you have corrections, please send them in.
|6 bolt holes,
3 - 6 evenly spaced
|Shimano, SRAM, 3T
|Campagnolo, FSA, Wolf Tooth
|3 bolt holes,
3 - 6 unevenly spaced
Click on the link to open the PDF file. Print the file out, being sure to set the printer for No Scaling or 100% so the page will print out at the correct size. Check the print size using the 5 inch - 127mm vertical and horizontal scales in the drawing. Because most printers pull paper through, the vertical dimension may be slightly inaccurate. If this is a problem, use another printer.
To measure a chainring, lay it down centered on the large circles at the outside of the printout. If the chainring has an even number of teeth, the numbered circle that is just barely hidden at the bottom of the gap between teeth gives the tooth count. The circle that is visible partway up between the teeth is for a chainring with two more teeth.. If the chainring has an odd number of teeth, the smallest circle which you can see between the teeth is for a chainring one tooth larger. Some of the smallest tooth counts couldn't be shown, because bolt-circle holes would cover them up. But then, teeth of these small chain rings are easy to count -- see the trick here.
To find the bolt-circle diameter, keep the chainring centered on the drawing, and rotate it until the same number shows in two of the small numbered circles. This is the bolt-circle diameter in millimeters. Remaining bolt holes should also align over small circles.
The drawings for unevenly spaced bolt holes also show the direction of the crank enforced by the uneven spacing. Many chainrings are marked to show the direction of the crank, and knowing it will speed the identification of a chainring.
You may have to check both drawings for unevenly spaced chainrings to identify a chainring. The many bolt patterns made it necessary to separate these chainrings by brand rather than the number of bolt holes.
Be especially careful if a bolt circle for a 3-or 5-bolt chainring measures at 85mm or 86mm, as they differ by only 1mm.
Last Updated: by John Allen