The Engineering Toolbox and Cavco have detailed online charts that show the exact measurements of different classes of flange bolts. BoltDepot.com has a chart that shows a visual of different flange bolts, gives product examples for each types and gives basic information about bolt grades.
The measurement charts from The Engineering Toolbox for flange bolts show the pipe size, the diameter of the flange, the number of bolts, the diameter of bolts, the diameter of the bolt holes and the bolt circle size. Cavco's charts also show different measurements for machine bolts and stud bolts. The charts at BoltDepot.com explain which bolt products are useful for automotive use, general hardware use and which are corrosive resistant.