7 CFR § 51.3212 - Metric conversion table.

Inches	Millimeters (mm)
1/8	3.2
1/4	6.4
3/8	9.5
1/2	12.7
5/8	15.9
3/4	19.1
7/8	22.2
1	25.4
1 1/4	31.8
1 1/2	38.1
1 3/4	44.5
2	50.8
2 1/2	63.5
2 3/4	69.9
3	76.2
3 1/2	88.9
4	101.6