This has Kluson tuners that appear to be 1940s. The case is from around the 50s. There may be something a bit odd at the nut while there is a gap at the heel. Anyway, two pickguards and a complete mystery to me. The headstock and heel shape do suggest United but this mandolin appears to have a two piece back- it is quite nicely made.
https://www.ebay.com/itm/Custom-CB-M....c100667.m2042
Bookmarks