Screws that screw downwards from the inside of the frame and press against the rail? Grub screws, still #10-32 thread, as are the clamping screws on quite a lot of the expanding-dovetail type rails such as CP and Eclipse dovetail rails.
EDIT: Pictures may come in handy:
Socket Head Cap Screw:
Countersunk Head Cap Screw:
Grub Screw:
I have a few sizes of all of the above, so if you can say which you need I may be able to help