.50 drill bit = 8mm rubber grommet
A 3/16 drill bit.
An 'O' drill bit is a decimal size, 0.3160 inch, which is between 5/16 and 21/64 on the fractional inch scale.
The 'R' drill is 0.339 inch, which converts to just a tiny bit less than 11/32 of an inch
It's 0.1160 of an inch, or a tiny,tiny bit less than 1/8 inch.
A 4 mm drill bit is equivalent to 5/32 inch.
That size is correctly 0.375, and is equal to 3/8 of an inch.
For a clearance hole you need a 9/64 drill bit.
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.
The width of a drill bit is it's size, measured in mm or in fractions of inch.
You are not expressing the size correctly. -There is NO 054. -If you mean 0.054 of an inch, then the nearest drill size is a #54 drill, which is 1.397 mm thick.
5.105 is 0.201 inch , or #7 on drill gauge. Both are common drill bits.