According to TMC RP 240, your wheels should have a finished mil thickness of no more than 3.5 mils on the mounting surface. This can be tested by using a mil thickness gauge mid-way between the bolt holes along the mounting area, on both sides of the wheel. It’s also important to avoid any runs or excessive coatings, as this could cause the joint to settle in and lead to loose fasteners, premature wear, or even the loss of a wheel. Your service provider should check the powder coating thickness of each wheel it refinishes.