mm is not a number and so, in itself, it cannot have a fraction form.
1.5 mm is equivalent to approximately 0.059 inches, which can be expressed as 59/1000 in fraction form.
1 inch = 25.4 mm so 8 mm = 8/25.4 inches = 40/127 inches.
There is no intrinsic fraction for MM. If something is measured as a whole number of MM then it is an integer value, not a fraction.
To convert 60 mm to eighths of a millimeter, first convert 60 mm to inches, as there are 25.4 mm in an inch. Thus, 60 mm is approximately 2.36 inches. Since there are 8 eighths in a whole, multiply 2.36 by 8, which gives you about 18.88 eighths. So, 60 mm can be expressed as approximately 19/8 in fraction form.
1 inch = 2.5 cm 7.7 mm = 0.77 cm (10 mm in 1 cm) So 0.77/2.5 = 308/1000 = 308 thousandths of an inch.
7/2 mm
The fractional part of 1.5 mm is 0.5 mm. However, if you want 1.5 mm as a fraction of some other quantity then you need to specify that second quantity.
It is 5/2 mm as an improper fraction
1 7/20 mm
A mm is 1/1000 of a meter
3.5 mm as an improper fraction is 7/2 mm
7/1 mm or 14/2 mm etc