Two friction bushing systems are widely available – KWM and Bergeon. The KWM is preferable due to the smaller outside diameter (less material removed from the clock plate, yet the bushing has enough material to be strong). Also, the KWM bushings for American clocks are available with longer pivot area (some of the Bergeon bushings are chamfered out way too much) allowing less wear to the pivot and bushing. Also, many suppliers (such as R & M Imports) offer KWM size bushings made in USA (called the American system) instead of Germany, that are made of harder brass.
Bronze bushings are available in some systems, but I don’t use them. I have found that brass bushings give excellent service, provided that the pivots are polished as part of the repair job.
The thing I really hate about Bergeon bushings, is that once they have been installed in a clock, you can’t easily use a KWM bushing, as the hole in the plate is too large! If every repair shop would use KWM bushings, future repairs on these clocks would be easy. Some shops custom fit bushings, which look nice, but make future repairs more difficult. KWM bushings can be chamfered to be invisible in French clocks, yet still be easily changed in the future. In American antique clocks, I prefer 1.8 mm height bushings which protrude above the plate, and give a longer bearing area to reduce future pivot and bushing wear.
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