This is an FT-87-W. I got 27.9 mH from 60 turns of #24 wire. See <http://www.mag-inc.com/products/ferrite-cores/ferrite-toroids> and <http://www.mag-inc.com/products/ferrite-cores/w-material>. Magnetics, Inc says "W material is a high permeability material used for EMI/RMI suppression, common mode chokes, pulse and broadband transformers." They might be a bit lossy in a switched mode power supply, but I think they would make nice audio filter inductors, if you don't mind winding a zillion turns on a smallish toroid. Amidon sells them for $1.20 apiece.
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