Through-tool coolant systems, also known as through-spindle coolant systems, are systems plumbed to deliver coolant through passages inside the spindle and through the tool, directly to the cutting interface. Many of these are also high-pressure coolant systems, in which the operating pressure can be hundreds to several thousand psi (1 to 30 MPa)—pressures comparable to those used in hydraulic circuits. High-pressure through-spindle coolant systems require rotary unions that can withstand these pressures. Drill bits and endmills tailored for this use have small holes at the lips where the coolant shoots out. Various types of gun drills also use similar arrangements.