After many years screwing in and out of mounting plates, the threads on mounting plate thumbscrews can become worn or stripped. The thumbscrews are easily replaced in the laboratory or clinic and do not require that the instrument be returned to Whip Mix for repair. (Thumbscrew Item #110083)
When replacing, pull slightly up on the upper thumbscrews or slightly down on the lower thumbscrew to engage the threads of the threaded bushing. Then continue to unscrew until the thumbscrew is free from the articulator.
To replace, engage the threads of the threaded bushing with the new thumbscrew and screw down until the thumbscrew drops through to its correct position, ready to engage the mounting plate.
If you find that while removing the thumbscrew or trying to replace it, that the threads on the threaded bushing are damaged, the articulator should be returned to the factory for replacement of the bushing. This replacement requires a special tool to press the bushing out and then place the replacement into the upper or lower member of the articulator. Because of this process, the threaded bushings are not for sale as an outside replacement part.
If you are tired of screwing on mounting plates, you can convert your COMBI and COMBI II articulators to magnetic mounting plates by using the DENAR Magnetic Mounting System. These Denar Articulator parts consists of the Converter Plates (ITEM# 20002367) and the Magnetic Disposable Mounting Plates (ITEM# 20002368) in a bag of 20 plates or in a bag of 100 plates (ITEM# 20002369).
Simply screw the converter plates onto the upper and lower members of the articulator as you would a standard screw mounting plate. The new magnetic disposable plates will snap into the magnetic converters. Now mount your models as you would normally. You will lose some inter-frame distance of about 1.5cm, but will be able to mount most cases without issue.