US (inch) screws are commonly* classified as either Coarse or Fine thread by the 'Threads Per Inch' (TPI) measured along the fastener.  TPI is only used on US screws, as metric use a very different Thread Pitch classification and are not interchangeable.

Below is a table that shows screw sizes and the relevant UNC and UNF versions (if any).  Some are very common, others are not (I'm looking at you #5-44).  

Screw Size Threads Per Inch (TPI.)
Coarse / UNC Fine / UNF
#0 - 80
#1 64 72
#2 56 64
#3 48 56
#4 40 48
#5 40 44
#6 32 40
#8 32 36
#10 24 32
#12 24 28
1/4" 20 28
5/16" 18 24
3/8" 16 24
7/16" 14 20
1/2" 13 20
9/16" 12 18
5/8" 11 18
3/4" 10 16
7/8" 9 14
1" 8 12
1-1/8" 7 12
1-1/4" 7 12
1-1/2" 6 12

* Note - in addition to UNC (Coarse Thread) and UNF (Fine Thread) there is a much less common UNEF (extra fine) thread that is not listed here as it really is not widely used in practice.