There is also a small roll pin that needs to be seated into a tight fitting slot in the extractor. It relocates the insert to the regulated position the next time you use it. The two sliding lugs are to regulate the barrel, and as you will notice, they are not opposed 180 degrees, so you will have windage and elevation adjustment by moving them up and down. You do need to make the small round slot in the extractor before you try to seat and tighten the insert with a square key, or you'll damage the roll pin.

I always install the inserts into the right barrel, as that has the set trigger.