What screws to use for mounting a Korean Joystick in my HRAP 3?

Ok so having installed my joystick, everything works just fine. Only thing is that the screws that I am using (I got at my local hardware store) will go in about half way and then just stop turning.. so I had to use duct tape for the time being to secure it just so I could test if the thing worked. So any suggestions? The second pic are the screws I used to secure the joystick (I am using the 4 in the corner, not the middle 2 points that fastened the JLF).