Sorry, Arline. When you get your smoker, set it on your cart. With a pencil, mark around each leg. Then, draw diagonal lines to find the center of the square (sorry to bring geometry into this), then drill 4 holes slightly larger than the threaded ends of the casters. You can take one of your casters to Lowe's or Home Depot, and have them tell you the thread pattern. You will then buy 4 pan head machine screws that size, with flat washers. No need to measure anything, just use your actual smoker as a guide (all of them could be slightly off, due to manufacturing).
Once you have your screws, place the smoker on the cart, lining it up with your original marks. Use one screw & flat washer, per hole, from the bottom of the carts top, to secure your smoker. The SI cart works the same way. Hope this helps more!