Pup joints and varying lengths of tubing and casing are used to adjust the production string length as close as possible to the desired value. Then the adjustable union or joint is installed, rotationally adjusted, and locked to the desired make up length. In dual completions, the tool can be used to adjust the length of the short string. The adjustable unions and joints facilitate tubing space out when completing a well. In most completions, the length of tubing available at surface is not enough for proper wellhead installation and operation.