Everyone who had to drill holes in the pipes or other parts of circular cross-section, knows that this is a difficult task. The drill bit often slips with printed core labels, and the holes are not strictly diametrically. However, to facilitate this work and to improve the quality of the holes, a special conductor is a metal bar M-shaped cross section with a series of holes under the most frequently used drill bits. To make the fixture very easy; we only need to remember that the axes of the holes must coincide with the axial plane of the bar.
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