Bolts, Nuts, Lock Nuts and Washers

Bolts, Nuts, Lock Nuts and Washers

Threaded fasteners appear on nearly every assembly, and they are drawn to convention rather than to their true geometry — a real thread is a helix, and drawing it as one on every bolt would be unreadable and pointless.

Conventional thread representation. The crest of the thread is a continuous thick line; the root is a continuous thin line. On an external thread the thin line sits inside the outline; on an internal thread it sits outside the bore.

Hexagon heads and nuts. Drawn across corners in one view and across flats in the other. Standard proportions are based on the shank diameter D: width across flats ≈ 1.5D, head or nut thickness ≈ 0.8D.

Lock nuts are thinner than standard nuts and are fitted above the main nut, jammed against it.

Washers spread the load and protect the surface. Plain washers sit under the nut; spring washers resist loosening under vibration.

A critical convention: a bolt, nut, washer, key or shaft is never hatched when the cutting plane passes along its axis. They are solid, so sectioning them shows nothing — and hatching them makes the fastener disappear into the part it holds.

Core checkpoint: Threads and fasteners are drawn by convention. Learn the conventions; do not draw what a photograph would show.