After some research and head scratching we’ve been
able to determine that the thread sizes on the Marlin supplied oil
pressure and temp sensors are 1/8″x27 NPT. The thread size on the
engine for the temp sensor is 14mm x 1.5 and for the oil its 12mm x 1.5.
piece M12 x 1.5 for oil sensor, the adapter has the right thread for
the oil pressure sensor in the side, and the oil switch to go in the
bottom. The other M12 adapter is spare, didn’t need it as the T piece
had the right thread for the sensor. The M14 x 1.5 is for the temp
sensor. It replaces the brown one on the engine.