On vintage Flyers, TT Reps, etc., the brake rod and fittings should be 5/16″ BSCY 26tpi. On safety-critical items it is best to think that in the past 85-90 years the rod will have been bent, corroded, and perhaps replaced in an inferior material. Best practice is to renew the rod from a length of EN8 or similar steel, and have a very close look at clevises, split pins, etc.. Right-hand brake pedal bikes should in theory have a slot/groove in the edge of the gearbox tray to stop the brake rod rubbing on the tray. They can also rub on the underside of the gearbox, leaving a groove that occasionally wears into hole in the shell ! I’ve just repaired one !