Use this custom stand for visual inspection to make sure you mini arrows will fly straight. You can move the end pieces around to get the proper standoff. I designed this for use with FKG R8-ZZ 1/2"x1-1/8"x5/16" Deep Groove Ball Bearings, but I recommend something better that spins more freely than those. The less friction the bearings have the longer your arrows will spin so you can evaluate them. The bearings simply snap into place and are held securely if you are using this exact bearing. Infill doesn't really matter. Choose any material that it rigid enough to provide mechanical stability.