Fastener part numbering system explained:
The last 2 digits (XX) of the 4 digit fastener part number prefix (40XX-12345-12) indicates the standard stud size of the bolt or screw. For example, part 4006-01030-12 indicates a #6 stud diameter (.138") fastener.
The 2 digit part number suffix for bolts and screws (-12, -04, -16, etc) indicates the number of 1/16 inch length increments of the fastener. For example, part 4004-01003-04 indicates a screw that is 4/16 inch long or 1/4 inch long.
The middle 5 digits describe the fastener head style or other features.
Basic diameters and threads of Standard SAE (Society of American Engineers) numeric system small machine screws are shown below.
The diameters of machine screws are indicated with the number of threads per inch. Here is a list of common sizes in inches:
2-56: 0.0860 inch or 43/500 inch in diameter; 56 threads per inch
4-40: 0.1120 inch or 14/125 inch in diameter; 40 threads per inch
5-40: 0.1250 inch or 1/8 inch in diameter; 40 threads per inch
6-32: 0.1380 inch or 69/500 inch in diameter; 32 threads per inch
8-32: 0.1640 inch or 41/250 inch in diameter; 32 threads per inch
10-32: 0.1900 inch or 19/100 inch in diameter; 32 threads per inch
10-24: 0.1900 inch or 19/100 inch in diameter; 24 threads per inch
12-24: 0.2160 inch or 27/125 inch in diameter; 24 threads per inch