We are going to explain the function of the screw down crown.   What we have seen is that when someone gets their watch for the first time they will unscrew the crown on the watch to set the time and date. After they set the time and date, they just push it in. They are using a push in crown.
A Hook + Gaff watch uses a screw down crown.   What you have to do is apply a little bit of force and screw the crown, get it to take the threads, and screw it down tightly against the case. A screw down crown ensures you have all the confidence in the world that your watch is watertight.