I’m not sure the wisdom of adding a washer under an NPT-threaded fitting at all, nor under a straight threaded fitting not originally specified to have a washer (especially in an aviation or other highly regulated application).
I wonder if you could get by in some of those applications by having the tag in a grease zerk cap instead (installed after and without disturbing the zerk torque/seal).
On my airplane, I rotate grease cap colors as a visual check that all fittings were serviced during the annual inspection. It’s a multi-day affair with more than one mechanic plus me plus interruptions, so it’s not difficult to miss some. But if the cap is blue and this year’s color is red, you find it at final walk-around.
I wonder if you could get by in some of those applications by having the tag in a grease zerk cap instead (installed after and without disturbing the zerk torque/seal).
On my airplane, I rotate grease cap colors as a visual check that all fittings were serviced during the annual inspection. It’s a multi-day affair with more than one mechanic plus me plus interruptions, so it’s not difficult to miss some. But if the cap is blue and this year’s color is red, you find it at final walk-around.