These fixings are a type of machine screw that resembles the old "thumbscrew" but has a Philips screwdriver recess in the head so that you can tighten it with a screwdriver rather than having to turn it by hand (although it's still possible to do it by hand if you prefer). These fixings are approx 26mm long; the top part is approx 12mm x 10mm diameter, the threaded part is approx 14mm long. These fixings don't seem to fit anything other than their own captive threads apart from a very few vintage British banjos which have an almost identical thread.
The captive threads are no longer available but there are still a lot of banjos around that use this kind of resonator fixing; we will therefore continue to offer the thumbscrews as useful spare parts for those who may have mislaid or damaged the originals.
If anyone knows of a source for a captive thread of this type (approx 3/16" BSW), we would be glad to hear of it; the available products at the moment seem to be exclusively metric.
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