For the various sizes of tubing and wall thickness used in a hydraulic system, the inside diameter can be determined if it is remembered that the inside diameter equals the outside diameter less __________.

In USCG Marine Engineering General Subjects, for engine room systems involving 'For the various sizes of tubing and wall thickness used in a hydraulic system, the inside diameter can be determined if it is remembered that the inside diameter equals the outside diameter less', the standard operating requirement is: '2 times the wall thickness'.