Nominal Pipe Size (NPS) is a North American set of standard sizes for pipe where specific pipe is identified by pipe diameter and another non-dimensional number for wall thickness referred to as the Schedule – for example – “2-inch diameter pipe, Schedule 40”).
From the perspective of a modeler the important thing is the OD of the pipe.
- For NPS 1⁄8 to 12, the NPS and OD values are different. For example, the OD of an NPS 12 pipe is actually 12.75 inches (324 mm)
- For NPS 14 and up, the NPS and OD values are equal. In other words, an NPS 14 pipe is actually 14 inches (360 mm) OD.
The reason for the discrepancy for NPS 1⁄8 to 12 inches is that these NPS values were originally set to give the same inside diameter (ID) based on wall thicknesses standard at the time. However, as the set of available wall thicknesses evolved, the ID changed and NPS became only indirectly related to ID and OD.
Here’s an assortment of tubing and wire that I found which should be “Good Nuff” for modeling pipe in O scale. I’ve included sources readily available either online or at a box store. If you can think of additional sources let me know so I can include them.
O_Scale_Pipe_Data_v3
Evergreen Tubing …
I have over time made a lot of fittings for Evergreen tubing. The methodology remains the same for all sizes by creating a small stud on the fitting that will slip into the appropriate size Evergreen tubing. Here I have a 90° elbow with a 1.7 mm stud that fits into Evergreen No. 224 tubing. This has a 1.8 mm ID. Sizes of the tubing is nominal .. why the 0.1 mm small stud.
The fitting has both the flange of the elbow itself as well as the flange for the attached pipe (tubing).