Momala,
The little screw go into a piece of some kind of hard plastic material. You don't tighten the screws real tight, so I think it will last just fine. I haven't used mine that much, but I haven't had any problems so far. I use my Accuquilt cutter for the long strips, then use the Adj. locking ruler to cut into Triangles once I have sewing them together. Unless you are cutting lots of different sizes, you may not even move the adj. screw part.
I don't know if any of you have the o"lipfa ruler. It works about like that except you can move the adj. stop part.
Something else a person can do if you are wanting the adj part stop. Take a ruler that you are using, get double sticky tape and tape a piece of mole for the stop. Then you just butt the ruler to the fabric. The sticky tape is very temp, but it does work.