Do you mean what is the abbreviation for millimeter? Because that is "mm". When you write units in fractions, you will probably want to use the abbreviation.
It is forty nine thousandths of a millimeter.
One-tenth
1/1000
Forty-nine thousandths millimeter.
1.000 millimeter (as many zeros as you want after the decimal point)
A millimeter in fraction form to a meter is 1/1000.
1/1000A millimeter is 1/1000 or 0.001 of a meter.
1/1,000,000
It is forty nine thousandths of a millimeter.
One thousandth.
One-tenth
0.5mm
Forty-nine thousandths millimeter.
1/1000
1.000 millimeter (as many zeros as you want after the decimal point)
A millimeter (mm) is a fraction of a centimeter (cm).
The answer will depend on what the fraction is.