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Definitions For Pipes, Tubes, & Fittings

Term Definition
Close Shortest nipple - no pipe between threads.
Dropear Has a nailing flange on the back of the fitting.
FHT Female hose threads (garden hose).
Fips Female pipe threads on the inside of the fitting.
Flare A compression fitting used with metal tubing, typically soft copper.
Hyset Has a nailing flange on the front of the fitting.
I.D. The abbreviation for the "Inside Diameter". It is the measurement of the maximum inside to inside measurement across the inside of a pipe or tube.
MHT Male hose threads (garden hose).
Mips Male pipe threads on the outside of the fitting.
Nominal used to describe copper pipe and fittings in the plumbing industry. Refers to the inside diameter of the pipe which varies by thickness of the pipe. The outside is a constant size and is always 1/8" larger than the nominal size. For example, 1/2" nominal is always 5/8" O.D.
O.D. The abbreviation for the "Outside Diameter". It is the measurement of maximum outside to outside measurement across the outside of a pipe or tube.
Ovality No pipe or tube is perfectly round. Ovality is used to quantify how out of round (think squished) a pipe or tube is. Ovality is simply the difference between the widest outside diameter (O.D.) you can measure on a piece of pipe or tube minus the smallest outside diameter (O.D.) you can measure on the same piece of pipe or tube. For example, a tube could have an average outside diameter of 4.00 inches but it could have a maximum O.D. measurement of 4.015 inches at one point and a minimum O.D. measurement of 3.985 inches at another point. Its ovality would be .030 inches, which is the maximum O.D. - minimum O.D. or (4.015" - 3.985" = .030").
Pipe & Tube
The terms Pipe and Tube are used interchangeably every day - even by the experts, but they are different. Tubes are the most straight forward in that the outside diameter of say a 2" tube is truly 2". Pipe on the other hand was originally designed to carry water on its inside so a 2" pipe roughly references the inside diameter of the pipe - not the outside diameter.
Potable In reference to water is that potable means it is drinkable water. Water that is suitable for human consumption.
PVC The abbreviation for Polyvinyl Chloride is used today for cold water pipe (outside/underground) as well as for sewers, drains, wastes, venting pipes, and fitting. Flexible PVD pipe is also available and quit.
Saddle Afitting that attaches to the side of the pipe.
Reducer A fitting that connects pipes of different sizes together.
or Sch.
The Schedule designation is an industry standard classification that basically tells you how thick the wall is for any size of the pipe. The most common schedules are Sch. 40 and Sch. 80. The higher the schedule number the thicker the wall is with Sch. 40 being the thinner and Sch. 80 being the thicker. For example, 2" pipe all has an O.D. of 2.375" but schedule 40 has a wall thickness of .154" and 2" schedule 80 has a wall thickness of .218". Also note that a schedule 40 wall thickness is different for every different size of the pipe. A 2" schedule 40 pipe does not have the same wall thickness as a 3" schedule 40 pipe. The 2" schedule 40 has a wall thickness of .154" but the 3" schedule 40 has a .216" thickness.
SDR The abbreviation for Standard Dimension Ration. It is a convenient means for defining the minimum wall thickness for pipe (not tube). It is equal to the actual pipe diameter (not the nominal pipe size) divided by the wall thickness. For example, 2" pipe, which has an actual O.D. of 2.375" with a wall thickness of .091", would have an SDR value of (2.375" / .091") or an SDR of 26. In the reverse, by knowing the pipe size and SDR number, you can calculate the minimum wall thickness. For example, 3" SDR 21 pipe which has an actual O.D. of 3.500" would have a minimum wall thickness equal to (3.500" / 21) or .165". It is important to note the wall calculated is the minimum wall thickness. In the case of the 3" SDR 21 pipe, we would actually extrude the wall at .177" with a tolerance of plus or minus (+/-) .012". This would mean that the walls could run in spec from a maximum of .177" + .012" or .189" to a minimum .177" - .012" or .165" which is the number as calculated by the SDR ratio.
S or Slip A regular hub. The pipe glues into this type of connection (same O.D. as coupling).
Spigot or SP The same size as the pipe. Glues into another fitting.
Street Elbow An elbow fitting that has a male end (same size as pipe) on one side and a female end (pipe fits inside this size) on the other side.

Nominal Size To OD Size Conversion Table
O.D. Of Pipe 1/4" 3/8" 1/2" 5/8" 3/4" 7/8" 1-1/8" 1-3/8" 1-5/8" 2-1/8"
Nominal Pipe Size 1/8" 1/4" 3/8" 1/2" 5/8" 3/4" 1" 1-1/4" 1-1/2" 2"

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