7 CFR § 51.1538 - Metric conversion table.

Inches	Millimeters (mm)
1/8 equals	3.2
1/4 equals	6.4
3/8 equals	9.5
1/2 equals	12.7
5/8 equals	15.9
3/4 equals	19.1
7/8 equals	22.2
1 equals	25.4
1 1/4 equals	31.8
1 1/2 equals	38.1
1 3/4 equals	44.5
2 equals	50.8
3 equals	76.2
4 equals	101.6