12 grader new temp gauge problems

I bought a non-cat water temp gauge part no. 200-5235 for my 8T5057 grader. The bulb that goes into the head came with an adapter which appears to be 1/2" pipe thread. The original temp adapter (8B9494) is a 7/8" course straight thread with a copper gasket, that goes into the head and 5/8" fine thread internal to hold the bulb tight . If I use my original adapter and the new bulb nut, I can not get the new bulb to tighten up.

Do I need a different adapter or do I need to re-thread the head to a pipe thread, or get a different part number gauge?

Thanks,
Muzz

I'd be looking for the proper gauge.