These are milled billet aluminum, we have used these for the coolant sensor locations from a mk3, mk4, mk5. and mk6. This allows you to install a mk1 sensor in with your motor swap to regain the function of your mk1 cluster after a motor swap.
They are threaded to m10x1, and many aftermarket sensors will fit as well, allowing you to install aftermarket gauges into your mk3/4/5/6 if you needed.
Installation is very simple, install the sensor into the adapter, install into the coolant flange with the provided o-ring and clip, attach the grounding wire to the nearest grounding point on the motor. Attach the signal wire to the sensor and check your gauge function.