a spot welding fixture for holding worpieces in correct orientation has a water cooled aluminum body processed to have an aluminum oxide coating . the coating electrically insulates the body but provides good thermal conductivity so that a fixed electrode on the fixture body can be cooled by the body but no electrical shorts occur . locating elements on the fixture are likewise insulated to prevent weld current from straying from intended paths . the coating is formed by immersing the aluminum body in sulfuric acid at 23 degrees fahrenheit after all features have been machined into the body .