These plastic spin welding machines can be used to make car filters, spin welding machines, RO water purifier filters, water jugs, and round workpieces. Spin welding is a technique for joining circular thermoplastic parts that involves spinning the part surfaces together under pressure. One portion is held still in a fixture while the other is rotated under pressure against it. Because of the frictional heat created, the part interfaces melt and fuse together, forming a strong, hermetic seal.