How to not crack gelcoat

[nipper]

Thanks, Destroyer, but I really do not have good tools, I am sorry to say, and I certainly do not have a set of calipers. When you say 75% thread, does that mean that the hole I drill should be 25% of the size of the size of the screw or does that mean the hole should be 75% of the diameter of the screw. Sorry to be an idiot on this, but, admittedly, I am.

I guess that leads me to another question. Should I have the curtain made first and then position the screws with snaps according to where they are on the curtain or vice versa. I am thinking curtain first then place the screws/snaps to fit the curtain, but I am not sure. And if I am right, I guess that leads to yet another question. How tightly should I stretch the curtain when determining where to place the screws/snaps into the sides of the liner. And now that I think of it, yet another question. Assuming the curtain is a rectangle approximately 5' long by 2 1/2', is there a particular sequence I should follow in placing the screws and snaps into the liner? For example, should I go corner to corner, then corner to corner again and fill in the snaps between the corners or some other sequence? I want to avoid "puckers" if I can!