Bicycle chainrings have between three and six bolt holes to attach them to the crank, spaced around in a circle. The table below gives bolt-circle dimensions for the main brands using each bolt pattern. Aftermarket and less prominent brands tend to use the same bolt-circle patterns as the main brands, for compatibility.
Direct measurement of the bolt-circle diameter is often not possible with a ruler. No two of an odd number of holes are directly opposite another. 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, and these identify the bolt-circle diameter.
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.
The bolt-circle diameter doesn't tell the whole story about compatibility if you mix and match parts. Sometimes you can fix the problem by installing a chainring inside-out or using washers to adjust spacing. Check for these issues:
After measuring 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. Wolf Tooth also offers a guide to direct-mount (spiderless) chainrings at the bottom of a page on its Web site..
All bolt-circle patterns 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 ramps and pins. Unevenly-spaced bolt holes make it impossible to turn chainrings to increase wear life, and some patterns reflect mere cussedness -- "brand lock". Please see the page at pardo.net discussing technical, pricing and availability issues for chainrings with unevenly-spaced bolt holes.
Bolt-hole spacing dimensions here for evenly-spaced holes reflect exact (known) angles. We have given dimensions reflecting an integer number of degrees, probably correct, for unevenly-spaced holes. Measured angles for all Shimano unevenly-spaced holes 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. Wolf Tooth and FSA sell chainrings to fit other manufacturers' cranks but also chainrings that fit only their own cranks and direct-mount spiders.
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.
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||84.3, 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.
Dimensions 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