It is hard to tell from the picture. But it looks tapered, to my eyes. If you have calipers, measure the OD of the threads at the tip and near gauge. If it is parallel threads, there should be an O-ring inside the gauge block to seal against. My SAM came with a parallel style gauge and had tape on the threads. Not sure why. If it is NPT, the gauge block should be black and made of steel. There would be no bottom or O-ring.