Cisco network equipment, being American, use Phillips cross-point screws for the case and bracket mounting screws. The NM and WIC modules, however, are slightly different, using a slotted-Phillips, or Borneo® screwdriver. These are available in the US from, amongst other places, Menards (SKU: 2377751). In the UK there is a comprehensive Facom range available from Machine Mart, you will need Item No: 040211109.
Use the wrong one and you risk damaging the screws or your screwdriver!