Originally Posted by Zat_Zuma

Measure the thread pitch, (27 not 28) double check with the thread die and triple checked with a 1/8NPT & 1/8BSP fittings. It fits with the NPT and didn't fit the BSP thread. Plus the BSP thread is far more tapered than the NPT thread. It's quite easy to tell the difference when they are side by side. It's quite easy to figure out if you have the right tools and measurement equipment.

Not to mention since the DEFi oil pressure gauge sensor point is already installed with the OEM oil pressure sensor with a 1/8" NPT Tee fitting.
This is how I know for sure and can guarantee that it is a 1/8" NPT.