Archimedes' screw pipe does not need to be perfectly watertight, as long as the amount of water being scooped with each turn is large compared to the amount of water leaking out of each section of the screw per turn. If water from one section leaks into the next lower one, it will be transferred upwards by the next segment of the screw. In some designs, the screw is fused to the casing and they both rotate together, instead of the screw turning within a stationary casing. The screw could be sealed to the casing with pitch resin or other adhesive, or
Screw So, as a general rule, when buying a packet of "screws" nuts would not be expected to be included, but bolts are often sold with matching nuts. Part of the confusion over this is likely due to regional or dialectical differences. "Machinery's Handbook" describes the distinction as follows: This distinction is consistent with ASME B18.2.1 and some dictionary definitions for "screw" and "bolt". The issue of what is a screw and what is a bolt is not completely resolved with "Machinery's Handbook" distinction, however, because of confounding terms, the ambiguous nature of some parts of the distinction, and usage variations.