Depends on the diameter of the conduit. Try for 1/4" larger diameter drill bit.
A # 30 drill bit is 0.1285 inch, or fractionally more than a 1/8 bit.
A hand drill is scommonly used for holes under 1/4 in in diameterANS 2 - The diameter is simply the width of the drill bit from side to side.
With a micrometer.
Drill bits not only come in fractional number sizes they also come in letter sizes. The F size drill bit is .257 thousandths of an inch in diameter. A 1/4 inch drill bit is .250 thousandths of an inch in diameter, so size F is .007 thousandths of an inch bigger than a 1/4 inch drill bit.
For all practical purposes an 8mm drill is equal to 5/16 inch.
The measurement of a drill bit is taken across it's diameter. They go from very tiny, right up to inch sizes and are measured in metric or SAE,
I drill a pilot hole the size of the 'barrel' of the screw. -I always use a combination drill bit for sinking screwheads. The first part of the bit is the diameter of the 'barrel' of the screw and the step, one inch higher is the size of that screw's head. (The barrel is the diameter inside threads) -I have a set of these drill bits for #6, #8, and #10 screws and they are great.
A 3/16 drill bit.
11mm is almost exactly 7/16 inch.
A core drill is a drill specifically designed to remove a cylinder of material, much like a hole saw. The material left inside the drill bit is referred to as the core. Diamond core bit is commonly used in construction to create holes for pipes, manholes, and other large-diameter penetrations in concrete or stone.
metal drill bit has a finer point