It's about 4.8 mm.
It is 35/64
5 mm dia drill bit
The closest SAE size to 4.5 mm is 11/64.
Surprisingly enough- a 6 mm drill bit, or if you don't have one,1/4 drill bit will do.
I would use a 10 mm drill bit.
A 4 mm drill bit is equivalent to 5/32 inch.
2.25 mm is 3/32 inch
4.5 mm is close enough to 3/16 to use that if you don't have a 4.5 drill bit
A 5 mm drill bit is equal to 7/64, or for all practical purposes, 3/16 inch.
.50 drill bit = 8mm rubber grommet
The width of a drill bit is it's size, measured in mm or in fractions of inch.