Hmmmm. My TTB nuts threaded right on my 79 RA arms. Differences in years I guess...
At any rate there are only 4 combos for the nut. Standard, Metric, Coarse, Fine. Yours will not be Metric(I guess), nor Fine thread. So hence you need a Coarse-Standard 1 1/8" or close to. Spend $20 on nuts...