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From the first set of sizes given I’d say with 99% certainty that it is indeed 1/8BSP.

Logic says that the other size should be 1/4BSP however the nominal size for 1/4BSP is 0.516” O.D. 0.425” core and 19tpi so it is somewhat undersize.

I suspect that at some time in the past someone has buggered up the original thread and has re-cut it with the nearest available die – in this case I’m guessing 7/16UNF.