These photo's are the mod I did to add additional cooking grate(s) to my WSM.
I took the grate to the hardware store and found the nuts, blots and washers that fit and then spaced them equally around the cooking grate.
I used an additional top cooking grate on the top grate for the mod. You can actually do two of these so that you will have four grates in the WSM, however, when I did mine and then used it to do a major chicken cook, I found air circulation hampered by the amount of chicken that will go on 4 grates.
This is a good mod though if you wanted to do ribs and lay them down or perhaps up to 9 pork butts at one time. That would be fun, wonder how long that would take.
Just a little under 4 inches between grates.
Thanks to Bill Hays for helping to locate the pics.
Treasurer, Great Lakes BBQAssociation
Rubbed, Smoked, and Sauced Competition BBQ Team-
22 1/2" WSM, 2 18 1/2" WSM's, 22 1/2" Weber Kettle