here are specialized lock screws which intersect at a right angle with the axis. This is specifically designated for a restricted space. The sizes for the internal treads range from M6 X 0.5P to M200X 3.0P. The MR Model with the thread is designed to face a squaring of 0.002 mm by the process of grinding. The MRZ or the MR Model is designed to face squaring of 0.005mm by turning the thread. The SR Model comes with a lesser thickness as well as a lesser outer diameter as compared to the MR series. However, it is at par with the ZM model.