1. n. [Drilling]

The part of the bit that includes a hole or opening for drilling fluid to exit. The hole is usually small (around 0.25 in in diameter) and the pressure of the fluid inside the bit is usually high, leading to a high exit velocity through the nozzles that creates a high-velocity jet below the nozzles. This high-velocity jet of fluid cleans both the bit teeth and the bottom of the hole. The sizes of the nozzles are usually measured in 1/32-in increments (although some are recorded in millimeters), are always reported in "thirty-seconds" of size (i.e., fractional denominators are not reduced), and usually range from 6/32 to 32/32.

See related terms: circulation system,  crossflow,  differential pressure,  exit velocity,  hydraulic horsepower,  jet,  jet velocity