HVAC copper tubing & pipe use Out-side-diameter in relation to their fitting

So, a 3/4″ air conditioning pipe needs a fitting that is 3/4″ Inside diameter

Ac pipe/tubing and fittings come in two thicknesses.

  1. “M” thickness is suitable for most common refrigerants the operate around   350 psi under

normal conditions

  1. “K” thickness is suitable for the higher pressure refrigerants such as 410a operating at 500 psi    under normal conditions

HVAC uses brazing at temperatures above 840°F

What is the nature of the brazing process

Unlike Soldering, the brazing rod material is drawn by heat. The capillary action draws the molten metal from the cooler area to the greatest heat.
We can define brazing as the joining of metals through the use of a heat and a filler metal. In this process, the melting temperature of the brazing filler metal is above 840° F (450° C), but in all cases below the melting point of the metals being joined.

The brazing process consists of the broad heating of the base metals to the point where the filler metal, applied to the joint area, will be melted and drawn by capillary action through the entire joint. After cooling, the brazed joint constitutes a strong metallurgical bond between the filler metal and the two base metals.

Two outstanding characteristics of a brazed joint are its high strength and the low heat at which it is made. A properly made brazed joint will generally be stronger than the metals being joined. And the temperature at which the joint is made is much lower than the melting temperature of the metals being joined.

A brazed joint “makes itself,” in the sense that capillary action, rather than operator manipulation, is responsible for flowing the filler metal completely through the joint. But even a properly designed joint can turn out imperfectly unless you follow correct brazing procedures.
Copper 45 & Copper 90Degree Elbows are used to change the direction of the flow of water 45 or 90 degrees. These fittings are connected directly to a copper pipe. CxC fittings have a flare connection on each end

Copper 45  & Copper 90Street Elbows are also used to change the direction of the flow of water 45 or 90 degrees. Unlike a standard elbow, a street elbow is only flared on one end allowing one end for insertion of a “like-sized” pipe while the opposite end can fit into a like-sized 2nd fitting. This allows an 180-degree turn with just two 90 degree fittings.

Couplings are used to connect two pieces of copper pipe together.

 

Reducing Couplers are used to connect two dissimilar diameter pipes

Caps are used to cover the outside end of a copper pipe.

Tee Fittings are used to either combine or split fluid flow. They are also used to connect pipes of different diameters or for changing the direction of pipe runs.

For More info on sizes see Common Terms and Size Chart Professional HVAC Technicians Glossary