That is a horizontal output transformer for a DuMont RA-101 or RA-102. These sets have a separate HV power supply, so it isn't really a flyback.
I am in need of one of these for restoration of our RA-101 custom:
http://www.earlytelevision.org/dumont_ra101.html
Please contact me at
[email protected]. I'll try to email you too.
Thanks.