A #6 screw has a diameter of 0.138". The second number denotes threads per inch (tpi), so a 6-48 screw is a #6 with 48 tpi. Industry standards for #6 screws are coarse (32 tpi), fine (40 tpi), and special (36 tpi). The 6-48 size is an oddball. You would need a number #31 drill bit to drill the hole and a # 25 if you wanted to clearance drill the hole for the screw. That doesn't leave a lot of meat in the hole if you break a screw off. Definitely not something that you could do with a simple hand drill.
Man it doesn't have to be this confusing for the average Joe. It doesn't matter what the thread pitch is on the ring cap screws. Just get a friggin drill bit large enough to drill off the head of the screw from the shaft of the screw and remove the scope ring caps. Then buy a new set of rings.
This isn't rocket science people.