Hello Mr Non-fixie,

The old thick TA chainring you have is a 1/8" chainring. Could have been for track use or for use on an old 3 speed derailleur bike. Requires a 1/8" chain as you know. SRAM PC-1 or a new old stock Sachs-Sedis SV3 probably your best bet. Check that the chain doesn't foul the derailleur or freewheel.

Reid