Bolt Basics (001): Thread Geometry and Classification
The bolted joint is one of the most widely used connection methods in mechanical engineering. Starting from the inclined-plane nature of a thread, this article sets out thread geometry and classification: the lead angle, the pitch, the pitch diameter d2, the minor diameter d3 and other key geometry parameters; common thread profiles and technical standards such as metric ISO coarse/fine, pipe threads and trapezoidal threads; and the functional distinction between fastening bolts, motion screws and sealing/adjusting bolts β laying the geometric groundwork for the later bolt strength calculation and pre-selection.