Measuring Pipe Techy

when measuring width of Pipe for Hydraulic pumps is it the outside or inside dimision?,,

I. D.
Angle Iron

PIPE is I.D.

TUBING is O.D.

THANX MF Poor, Tubing /pipe !.. That cleared Up All the confusion ...

Any more, Pipe anyway, its neither. From Wiki;

Pipe sizes can be confusing because the terminology may relate to historical dimensions. For example, a half-inch iron pipe does not have any dimension that is a half inch. Initially, a half inch pipe did have an inner diameter of 0.5 inches (13 mm)—but it also had thick walls. As technology improved, thinner walls became possible, but the outside diameter stayed the same so it could mate with existing older pipe, increasing the inner diameter beyond half an inch. The history of copper pipe is similar. In the 1930s, the pipe was designated by its internal diameter and a 1⁄16-inch (1.6 mm) wall thickness. Consequently, a 1-inch (25 mm) copper pipe had a 1+1⁄8-inch (28.58 mm) outside diameter. The outside diameter was the important dimension for mating with fittings. The wall thickness on modern copper is usually thinner than 1⁄16 inches (1.6 mm), so the internal diameter is only "nominal" rather than a controlling dimension.[5]

Now if you are looking to get some replacement hi pressure tubing I would sart by finding a chart on tubing and compair some measurements. If its pipe well, I know for a fact that 1.5" sch 40 "welded pipe" is; 1.9" OD, .145" wall, leaving the ID 1.61". Hi pressure tubing may be different, but pipe should follow the standard.
Welded pipe sizes

Not always; Pipe more than nominal 12" diameter is O.D.

Yeah copper tubing is not all measured the same either. See the link below.
Link

If you are dealing with hydraulic ports, you may have either pipe threads or machine threads. Machine threads will correspond with tubing size. JIC (Joint Industrial Commission (?) ), the two O-ring standards, and SAE flares use tubing threads. Tubing threads correspond with bolt threads. Some machine threads and pipe threads have the same threads per inch and can be close in OD. The site below may help in your hydraulic fitting selection.
Click me

When ever measuring pipe or tubing. Make certain the O.D. is larger than the I.D. or the hole will be on the outside of the pipe.