Abstract: The apparatus for boring a web of a section. The apparatus is provided with a boring device which is opposed perpendicular to the web of a clamped section and arm plates for supporting the boring device. The apparatus further has a clamping mechanism for clamping the section from each side thereof along the direction substantially parallel to the rotational axis of the boring device.

Abstract: A screw-bolt having crest-cut-off threads with their heights progressively decreased to not more than 3/4 times the basic height in the screwing up direction at a gradient ranging from 60/100 to 3/100 over that of the axial length of the threaded part of the bolt which is located between the unthreaded part and the complete thread upon setting up engagement with a nut therefor to allow a fraction of 0.1 to 0.2 unengaged with the nut, whereby the fatigue strength is increased in terms of the endurance limit from 6 kg/mm.sup.2 for the prior art bolt and nut to more than 11 kg/mm.sup.2 independently of whether SCM 14 or SNCM 5 steel is used in making the bolt and nut.