The PTA's are Large Shank.
When you measure the threads, (1.055" dia for small shank and 1.120" for large shank) those measurements are for the OD of the male threads on the barrel (aka-thread major diameter). Since you have a bare action you have the female threads and by measuring the inside of the action you are measuring the Minor diameter. If you add the thread depth to that measurement you will get the 1.120" of a large shank.
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