This tool works well with hand tools. If it is used with air tools, friction caused heat build-up will usually strip the all thread. Alway use the lubricant supplied with the bushings. Lubricants like WD-40 will wash the supplied lubricant off of the bushings. They should have trimmed edges with no over pour and a smooth surface.
Color can vary in a bushing set due to changes in formulations for specific locations.
They signify the polyurthane was not mixed properly during formulation. When a bushing has air bubbles in it the overall durometer is effected. You can guarentee the maker did not do this by design. 3560 Cadillac Ave.