1/8 BSPT to 1/8 NPT union. Used in our turbo kits for an oil feed. We pull out the factory oil pressure sensor and screw this in. Then you have a 1/8 NPT fitting on your car, which can be attached to a common 1/8 NPT tee. The brass threads on a tee are soft enough that the factory sensor can seal properly. 1990-95 and MSM blocks use a different fitting.
Not an easy part to find!