A 10 cm hole is almost 4 inches ! ! - IF you meant 10mm, then that's a little over 3/8 of an inch, or 13/32 for a clearance hole.
I use a 10 mm drill bit. -I suppose if you weren't too picky, you could use a 13/32 or a 7/16 drill bit instead.
10 mm drill.
For all practical purposes an 8mm drill is equal to 5/16 inch.
12mm
.0995"
.50196850"
Depends on the diameter of the conduit. Try for 1/4" larger diameter drill bit.
if the diameter 5/16 inches then you covert the 5/16 into 0.3125 inches. divide 5 by 16=0.3125 which is a little bigger than 0.3! ;)
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.
10 mm would be ideal. But 13/32" will work.
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.
I would use a 5/8 drill bit which is almost exactly 16mm.