We have reviewed the bolt circle diameter cribsheet, checked bolt-hole spacings using trigonometry and made some corrections. Apparently, the spacings were measured rather than calculated based on angles — and measurement is never exact! We have also added entries for several new patterns. Some of the new ones with uneven spacings had to be reverse-engineered from photos and, though we think that we have them right, we welcome feedback.
![Measuring bolt-circle diameter](http://cdn-0.sheldonbrown.com/blog/wp-content/uploads/2020/07/bcd-measure1smIMG_0672-600x378.jpg)
Measuring two holes away, right side to right side (or left side to left side) gives the most accurate result with a 5-bolt chainring.