E831-22 is the most common shackle sold with the 22-1221 springs.
For mounting bolts we use part C580412, a 5/8" X 4-1/2" (1 per spring) for the front of the spring and part C916412, a 9/16" X 4-1/2" (2 per spring) for the rear spring eyes and the shackle bolts.
The OEM does use metric bolts but the size difference is about 0.01" between the metric and the standard and there is a considerable price difference.
Feel free to call us at 1-800-358-4751 if you have any questions regarding the mounting parts or anything else about the 22-1221 leaf springs.