Screw pump different applications and handling fluids with varying characteristics. Each ‘screw pump' operates on the same basic principle of a screw turning to isolate a volume of fluid and convey it. However, the mechanical design of each is different. The primary difference is the number of screws: one, two, three or more. The screw pump was described by Archimedes on the occasion of his visit to Egypt. This suggests that the apparatus was unknown to the Greeks before Hellenistic times. A cuneiform inscription of Assyrian king Sennacherib (704–681 BC) has been interpreted by Stephanie Dalley to describe casting water screws in
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.