Bushings are designed to fuse the larger size into a socket fusion tee to make a quick reducing joint. - Example: take a SPT888, fuse a SPB86 into one side and you have a SPT886. Great fittings for an installer to have in his repertoire to quickly change sizes without needing a stick of pipe around. Life expectancy of 50+ years. Designed for geothermal installations. Can be connected with any IPS socket fusion iron.