Hello Flangetrade.
I have three catalogs on SAE hydraulic flanges that give dimensional data. The code they reference is SAE J518 code 61 & 62.
The companies are as follows:
Main Manufacturing Products (800-521-7918)these are square flanges.
Havit Hydraulic flanges distributed by Clinton Industries, Inc. (713-977-5521) these are slightly hexagonal in shape.
Anchor Flange Company (513-527-4444) these are slightly hexagonal, square/rectangular with sharp corners and square/rectangular with rounded corners.
I requested the info in 1993, so I am not sure how current the phone information is.
I hope this helps.