I have the BMW thermostat. It is 32mm on each port. That is 1 1/4 in. Having a big bypass port is odd, but not impossible. I used a 1 in. hose and stretched it over working the parts on a bench. Whenever I remove it to access parts of the car, I leave this hose on the part. You could use a reducer pipe, but I didn't want two more hose clamps.
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