They are already invaluable for many projects. I've used them from using them as the core of a 3D printed game ball (which can be used on a pool table) to testing floating tanks for ROVs. The balls were really accurate in measurement. They averaged about 1/10,000 inch larger with 4/10,000 inch being the worst, but for one project this worked perfectly. If I need more I will definitely buy from this seller again.