ASI "Wearables" says:
As you gain experience with digitizing, you’ll be able to tell just by looking which embroidery designs cross-pollinate better than others. Here are few guidelines to help you figure out whether a chest design will work well on a cap.
1. The design must be smaller than 2.25 inches tall to fit most hat frames, though some frames allow for designs as high as 2.5 inches. There are a few machines in the marketplace with a slightly larger sewing field for caps.
2. Designs with multiple borders around text rarely work well on caps.
3. Most caps today have a seam down the middle. This can play havoc with an embroidery design. For example, say you have the letter “I” in the middle of a design with no fill behind it. That letter will fall into the seam and look bad. This is never the digitizer’s fault. You wouldn’t park your car in the middle of a canal and expect it to float, right?
4. Detailed designs with tight registration can be very tricky on hats. The reality is that caps tend to move around in the hat frame, even when properly hooped. If a hat moves while it’s sewing a fill, there’s a good chance when the machine comes back around to stitch the border, it may not register.