I bought this tool to tighten the turnbuckle barrels on the chinrest brackets which I actually use to attach armrests to a couple of instruments (one De Faoite mandolin and one Shippey octave mandolin). It works fine on the OM armrest, which was made by Steve Bell (who I believe has stopped making them now), unfortunately it doesn't work on the mandolin armrest which was made using barrels from ABM-Mueller (who I believe have stopped making barrels, but had some old stock which they sold me), because these barrels have a slightly smaller diameter hole used to tighten the bracket. The diameter of the pin end of the Gewa chinrest tool is about 0.060". The Gewa tool is a lot better than the metal pin which Steve Bell provided to tighten the octave mandolin armrest, because the neck of the Gewa tool stops the pin end passing all the way through the barrel hole and scratching the instrument finish. The Gewa tool is solid metal so has a nice weight. It also has a hole at the other end so could probably be attached to keyring etc. So overall, although I can't use it on my ABM-Mueller brackets, I'm very please with the Gewa tool.
If you going to adjust your chin rest or install or remove one, you must buy this tool. Sure you can use something else that you may have hanging around like a pin or a nail, but the risk of damaging your violin is seriously increased. For me it's really not worth taking the risk and no matter how careful you are, just one small mistake means you can have a big scratch on your beautiful violin.
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