Install a black iron line for propane by cutting the pipe to length, threading it, wrapping the threads in plumbing tape and screwing it into the fittings. Always leak test each joint with a solution of dish soap and water. If bubbles form, take the line apart, tighten the joint, reassemble the line, and leak test again.
Tighten the jaws of a vice around the length, and cut the line using a pipe cutter with a rotary blade. To protect it from damage, add a few drops of good quality cutting oil as you use the cutter. After finishing the cut, remove the ridge the cutter leaves, and deburr the pipe.
Many plumbing shops provide threading services for pipes, but a ratchet style is available at many discount tool supplies for about the same price as threading five pipe ends. Add cutting oil when threading the pipe. Conserve the oil by placing a container with a screen under the threading tool to strain any filings from the lubricant.
Wrap the threads in plumbing tape by facing the pipe from the end and turning it around the pipe four times in a clockwise direction. Use two pipe wrenches, one on the pipe and the other on the fitting to connect the pipes, turning approximately two full turns after they are hand tight.