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 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.

Alternate Form: jet nozzle

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