The "flutes" are designed in the mount to keep the rings from moving forward and backwards. The rings clamp down on the base via a long screw. The body of which goes in that "flute". Turn the rings over and look at 'em.
The "6" in 6-48 is the size of machine screw that it is. The smaller the # the smaller diameter the screw. The next # (48), is the number of threads per inch. So a 6-48 would be smaller diameter that a 8-40 and also have finer threads. Some think that a 8-40 is stronger than a 6-48. Don't know either way, but I have never had a 6-48 shear off. If the rifle kicks that much it should probably be mounted to the top of your truck instead!
As far as the Torx wrenches, the bigger the # the bigger screw head and a T10 is smaller than a T30...JohnnyK.
"The only thing necessay for the triumph of evil is for good men to do nothing."