Question 287General Subjects - Assistant Engineer

The correct answer is A) thread series. The letters 'NPT' in the notation 1/8-27 NPT refer to the National Pipe Taper thread series, which is a commonly used standard for pipe fittings in the United States. The 'NPT' indicates that the threads on the fitting follow the NPT specification, which defines the thread profile, diameter, and other characteristics. The other options are incorrect because they do not accurately describe the meaning of the 'NPT' designation in this context. The thread profile, class of finish, and class of fit are not directly indicated by the 'NPT' letters in the given notation.