It all depends on the press. I have a Vastex V20000. I keep a few pairs in the shop to use with the numbering attachment or if I put a roller frame in the side clamp attachment and slide the screen out a bit. I use two. Depending on your press you can hook it around the screen clamps, which is what I do. I bring them both back to the opposite end of the press and clip it to those screen clamps. Remember If it is two tight when you drop the screen you are printing on it will pull the other print head up. I hope that makes some sort of sense.
Note: I have no problem with the press holding up screens unless I am doing something oddball. In which case I should swap out the shocks for heavy duty ones. So this is not a press issue. Are you looking to do this for an oddball job or are you just not able to hold regular screens up? If it is the latter you should look into replacing the springs/shocks.
