Most bicycle chainrings have between three and six bolt holes to attach them to the crank, spaced around a bolt circle. Templates linked from this page let you check the bolt-circle diameters (BCDs) -- and tooth counts directly. The tables at the bottom of this page give bolt-circle diameters for the major brands using each bolt pattern. Aftermarket and less prominent brands tend to use the same bolt-circle patterns as the major brands, for compatibility. You may use the tables the bolt circle by measuring with a ruler,
The bolt-circle diameter doesn't tell the whole story about chainring compatibility if you mix and match parts. There are issues with bolt-hole size, threading, tooth thickness, ramps and pins. Sometimes you can fix a problem by installing a chainring inside-out, using washers to adjust spacing, or drilling out bolt holes. Check for these issues:
After determining the BCD, you might check Wolf Tooth's Road and MTB chainring entries for details on newer 4- and 5-bolt chainrings; also RaceFace's compatibility table. Also, Wolf Tooth offers a guide to direct-mount (spiderless) chainrings at the bottom of a page on its Web site.
All chainrings used to have bolt holes equally spaced around the bolt circle. Starting around 2010, manufacturers introduced patterns with unevenly-spaced holes. These allow bolt heads of a small-diameter pattern to clear a thick crank, and enforce chainring orientation, important with chainrings that have ramps and pins to make shifting smoother. Chainring teeth wear unevenly, as power from pedaling has two peaks and two dips per rotation. Unevenly-spaced bolt holes prevent turning chainrings to increase wear life.Some patterns produce "brand lock" while others are available from more than one manufacturer. Wolf Tooth and FSA make chainrings to fit other manufacturers' cranks but also chainrings that fit only their own cranks. Please see the page at pardo.net discussing technical, pricing and availability issues for chainrings with unevenly-spaced bolt holes.
Bolt-hole spacing dimensions given here for evenly-spaced holes reflect exact angles calculated using trigonometry. For unevenly-spaced holes, we have used dimensions reflecting an integer number of degrees, probably correct. Measured angles for all Shimano unevenly-spaced holes of 4-bolt chainrings were so near 70 and 110 degrees that our numbers are almost certainly correct. SRAM had to be different, and its angles appear to be 72 degrees (same as with a 5-bolt chainring) and 108 degrees.
We are working on a Web page with more observations, and a description of how we generated the numbers in the table below. If you can provide corrections or additional information, please do! A Microsoft Excel workbook with calculations of all the dimensions used on this page is available on this site.
Many thanks to Ulrik Hansen for updates to the 4-bolt crank list.
Below are thumbnail images with clickable links to full-sized PDF templates to print out. These templates cover BCDs for all 4- and 5-bolt chainrings in commerical production, old and new, of which we know, for the types shown. More templates are on the way.
|6 bolt holes,
3 - 6 evenly spaced
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 it has an even number of teeth, the numbered circle that is just barely hidden at the bottom of the gap between chainrignl teeth is the chainring's tooth count. Rhe 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. Tooth counts for some of the smallest chainrings couldn't be given, because bolt-circle holes would cover them up. But then, teeth of these small chainrings are easy to count -- see the trick here.
To find the bolt-circle diameter, keep the chainwheel 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.
Be especially careful if a bolt circle for a 3-or 5-bolt chainring measures at 85mm or 86mm, or 4-bolt measures at 145m or 146mm, as they differ by only 1mm.
No two of an odd number of bolt holes are directly opposite another. Also, a protruding part may prevent direct measurement of the bolt-circle diameter of a crank spider. So, this page lists spacings between bolt holes which are not opposite one another, These can be measured with a ruler. The table at the bottom of this page gives the bolt-circle diameters that correspond to the measurements.
Many references describe distances between bolt holes as "center to center," but there is only empty space at the center of a hole! D'oh! Measuring from right side to right side or left side to left side is more reliable -- as shown in the photo below.
Measuring between non-adjacent holes reduces the likelihood of mistakes when differences are small. As an exercise, you may check the dimensions in the table farther down this page to identify the chainring in these photos, and then double-check against the brand-name stamp on the chainring.
Beware of near-matches! Measure!
The BCD is 1.414, 1/sin 45°, times the spacing between adjacent holes.
|Between adjacent holes
|146||44||103.2||Shimano XTR M960 Hollowtech 4-arm outer.|
|145||44||102.5||Campagnolo Super Record, Record, Chorus|
|120||36||84.9||SRAM 2 x 10 and XX. Threaded.|
|112||34||79.2||Shimano XTR M950, M952 4-arm middle/outer, Campagnolo inner.|
|110||34||77.8||FSA K-Force Light, Vero Pro|
|104||30||73.5||Shimano XT, LX 4-arm outer 12 SPD, Sugino MX350. Some are threaded. See RaceFace compatibility table.|
|102||32||72.1||Shimano 2003 XTR MX960 4-arm middle,|
|96||30||67.9||Shimano compact triple cranksets models M782, M672, M622, M612|
|94||30||66.5||SRAM XO1, X1, GX, NX|
|90||30||63.6||FSA: K-Force Modular Supercompact, Omega Pro, Powerbox Supercompact Stealth, Road Modular, Vero Pro|
|68||22||48.1||Shimano XTR M950, M952 4-arm inner, FSA Comet Modular|
|64||22||45.3||Shimano XTR M960, XT, LX 4-arm inner. See RaceFace compatibility table.|
|58||20||41.0||Sugino MX350 4-arm inner|
Measurements between adjacent holes of uneven patterns
|Between adjacent holes
|110||34||90.1, 63.1||Shimano Dura Ace 9000, Ultegra 6800, 105 5800, Tiagra 4703, 4700; Dura Ace with modification|
|110||34||89.0, 64.7||SRAM Apex 1. 72/108 degree angles. Shimano is 70, 110.|
|110||34||84.3, 77.8, 70.7||FSA Gossamer ABS, K-Force ABS, Powerbox, SL-K ABS|
|100||32||92.7, 64.3, 58.8||3T Torno. Must use 3T bolts. Looks like a 5-bolt pattern with one bolt missing.|
|96||30||78.6, 55.1||Shimano XT M8000, SLX M7000, Deore M6000, 10mm holes; XTR M9000 and M9020, M7 threaded holes.|
|96||36||73.5, 67.9, 61.7||FSA 96/68 SLK MTB ABS|
|76||26||65.8, 48.9||FSA Afterburner, Comet, K-Korce, SLK MTB ABS|
|76||25||62.3, 53.7, 48.9||SRAM XX1 11-speed, Cannondale, Specialized Stout. Threaded for M8 bolts.|
|68||22||52.1, 48.1, 43.7||FSA Comet MTB Modular, Comet triple, K-Force Modular, SL-K MTB Modular, V-Drive MTB Modular|
|64||22||52.4, 36.7||Shimano XT, SLX, XTR 11-speed with the "X" shaped bolt pattern.|
|Between adjacent holes
|Between non-adjacent holes (mm)||Application|
|151||44||88.8||143.6||Very old Campagnolo standard (pre '67) (Obsolete)|
|144||41||84.6||137.0||Old Campagnolo standard, still used for track; S-A FCT|
|135||39||79.4||128.4||Current Campagnolo standard|
|130||38||76.4||123.6||Standard Road double and triple (outer 2); S-A FCS|
|128||38||75.2||121.7||Nervar Sport, Star (Obsolete)|
|122||38||71.7||116.0||Stronglight 93, 101, 103, 104, 105 (Obsolete)|
|118||36||69.4||112.2||Ofmega, SR (Obsolete)|
|116||35||68.2||110.3||Old Campagnolo Gran Sport touring, Victory, Triomphe|
|110, 112||34||64.7, 65.2||104.6, 105.6||Campagnolo CT inner/middle/outer with one bolt at larger diameter behind crank|
|110||38||77.8, 70.7, 46.5||FSA K-Force ABS: uneven pattern, 4 bolt with extra bolt behind crank|
|110||33||64.7||104.6||Touring double, standard triple outer|
|102||32||60.0||97.0||Avocet triple inner (obsolete). Note, NOT same as Campagnolo.|
|100||31; 36||58.8||95.1||Merz adapter; Campagnolo triple inner (Obsolete)|
|94||29||55.3||89.4||Compact triple outer|
|93||28||58.5, 52.7, 55.3,
|Wolf Tooth "CAMO", barely noticeable uneven spacing, requires Wolf Tooth spider and bolts.
Angles are reverse-engineered from photos, may be slightly wrong.
|92||30||54.1||87.5||Shimano Dura-Ace triple inner|
|90||30||52.9||85.6||Edco, Mavic triple inner (old)|
|86||28||50.5||81.8||Stronglight 80, 99, 100, SR Apex (Obsolete). Chainwheels must be installed back to back, triple shifts poorly.|
|85||28||50.0||80.8||Old Shimano Deore, Takagi triple inner. (Obsolete)|
|80||26||47.0||76.1||Tevano (TA Campagnolo clone) triple inner. Bolts not interchangeable with others.|
|74||24||43.5||70.4||Standard ("full-sized") triple inner, used with 110 mm, 130 mm or 135 mm outer.|
|56||20||32.9||53.3||Sun Tour Compact granny (Obsolete)|
|50.4||n/a||29.6||47.9||TA Cyclotouriste, Criterium, Lambert, Shimano Deore, others: attachment for outer chainring; 7 mm holes.|
|6- and 3-Bolt Cranks/Chainwheels:
The BCD is:
2.000, 1/sin 30°, times the spacing between adjacent holes (6-bolt),
1.154 , 1/sin 60°, times the spacing between adjacent holes (3-bolt)
or non-adjacent holes (6 bolt)
60° apart (mm), 6-bolt
120° apart (mm)
|157||78.5||136.0||Several very old Euro models|
|152||43||76||131.6||TA Criterium bolts between outer chainwheel and others.|
|143||42||71.5||123.8||Lambert. Inner ring threaded.|
|140||40||121.2||Campagnolo Gran Sport inner|
|116||36||100.4||TA Professional (10 mm holes), many old Euro steel cranks|
|116||36||58||100.4||TA Randonneur: bolts are between outer chainwheel and others.|
|106||32||91.8||Sugino Maxy, others w/8mm holes, SR Apex w/10mm holes.|
|95||30||82.3||Shimano 600, 310|
|88.9 (3.5")||30?||77.0||Nicklin, Cross, Williams (very old)|
|86||28||74.5||FSA Pro MTB 386, Comet 386 MTB|
|85||28||73.6||SR Custom 3|
|80||26||40||69.2||TA Cyclotouriste, Lambert: bolts between outer chainwheel and others.|
|70||24||60.6||René Herse. 10mm holes.|
Last Updated: by John Allen