Metric Tube and Pipe Dies

Most tube and pipe manufacturers forge their materials to conform to the specifications of the International Standards Organization (ISO). While distributors refer to their products as metric sized, it may not measure according to how it’s labeled. For example: 25 mm tubing doesn’t usually have an outside diameter of 25 mm; it’s true outside diameter is 25.4 mm. You can refer to the chart below for the most common sizes. It’s important to know the actual outside diameter of your material before ordering a die. Using the example from above: if you order a 25 mm die and what you really have is 25.4 mm tubing, your material won’t fit in the die and you won’t be able to bend it. The outside diameter of the material must be measured with accurate calipers if you’re not sure what the true outside diameter is. Feel free to order one our standard dies by matching up your tubing to the charts below. In the case that you do have true metric tubing, we would be happy to make a custom die for you. If you’re still confused, give our expert technical sales team a call at +1 (813) 986-9000; we're happy to help you out with any questions.


Conversion from Metric to Inches
OD typically referred to as... Actual Outside Diameter (OD) in mm Actual Outside Diameter (OD) in inches, fraction Actual Outside Diameter (OD) in inches, decimal
6 mm Tubing 6.35 mm 1/4" 0.250"
9 mm Tubing 9.53 mm 3/8" 0.375"
12 mm Tubing 12.7 mm 1/2" 0.500"
15 mm Tubing 15.9 mm 5/8" 0.625"
19 mm Tubing 19.1 mm 3/4" 0.750"
22 mm Tubing 22.2 mm 7/8" 0.875"
25 mm Tubing 25.4 mm 1" 1.000"
28 mm Tubing 28.6 mm 1-1/8" 1.125"
31 mm Tubing 31.8 mm 1-1/4" 1.250"
35 mm Tubing 34.9 mm 1-3/8" 1.375"
38 mm Tubing 38.1 mm 1-1/2" 1.500"
41 mm Tubing 41.3 mm 1-5/8" 1.625"
45 mm tubing 44.5 mm 1-3/4" 1.750"
50 mm Tubing 50.8 mm 2" 2.000"
57 mm Tubing 57.2 mm 2-1/4" 2.250"
63 mm Tubing 63.5 mm 2-1/2" 2.500"


Nominal Pipe Size (NPS) is a North American set of standard sizes for pipes. The metric equivalent is Diameter Nominal (DN). The International Standards Organization defines the DN series of nominal sizes as an alphanumeric designation of size. It comprises the letters DN followed by a dimensionless whole number which is indirectly related to physical size, in millimeters, of the inside diameter or outside diameter. If you're a little confused about the difference between tube and pipe, check out our "What am I bending?" page for an explanation.

Conversion from Metric to Inches
Diameter Nominal (DN) Actual Outside Diameter (OD) in mm Nominal Pipe Size (NPS) Actual Outisde Diameter (OD) in inches
DN 8 13.72 mm NPS 1/4" 0.540"
DN 10 17.15 mm NPS 3/8" 0.675"
DN 15 21.34 mm NPS 1/2" 0.840"
DN 20 26.67 mm NPS 3/4" 1.050"
DN 25 33.40 mm NPS 1" 1.315"
DN 32 42.16 mm NPS 1-1/4" 1.660"
DN 40 48.26 mm NPS 1-1/2" 1.900"
DN 50 60.33 mm NPS 2" 2.375"