[RFI] FX1588 toroids?

[Dave_G4GED]

Hi
I have a number of 1.5 inch o/s diameter ferrite toroids which were bought at least 10 years ago.
They were supplied as being most suitable for winding RFI chokes.
They are stamped with the part #  FX1588 7748K. I've heard it said that's a Philips part # ?
I'm wondering wether they may be OK for winding Flag/Pennant transformers.
Wonder if anyone happens to know what Material type #  these are made from?
Tnx in advance
73 Dave G4GED