Marlco Thread Measuring Parallels B.S. Whitworth
The Thread Measuring Parallels represent what is probably the most simple and most flexible method of checking the effective diameter of external screw threads. They are manufactured to the highest degree of accuracy and to a specification certified by the National Physical Laboratory. Each pair covers a range of pitches irrespective of diameter or direction of thread. Thread Measuring Parallels are supplied as sets or individual pairs complete with plastic clips.