William, If the acorn nut is a common thread like 14x20 or 5/16x18, you might find one in a hardware store. A good hardware store usually has many flat boxes of odd fasteners. I am pretty sure you will be able to find a brass acorn nut there. If the size is right but the thread is wrong, you might also be able to re-thread it. Doug Gregg Classic Piano Doc Southold, NY
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