H&T stand for Hoch (high) and Tief (low), and if I remember correctly, moving the adjustment turret in the H direction moves the point of impact down and the T direction moves it up, the rationale being that if the POI is too high (H), then it needs to come down and vice versa. I have not seen a turret with two lock screws (one is the norm), but I would assume that that is what they are for.