Definition
Drilling Jar — A drilling jar is a BHA tool that delivers a sudden, high-impact hammer blow up or down the drill string to free stuck pipe, activating when tension or compression is worked into the string.
Also known as: drilling jar, jar, mechanical jar
What a drilling jar does
A drilling jar is placed in the bottomhole assembly as insurance against sticking. In normal drilling it transmits load and rotation like any other component, but when the string becomes stuck the driller can stretch or set down weight to “trip” the jar, releasing stored energy as a sharp impact blow. That hammer effect, amplified by an accelerator or bumper sub, jolts the stuck point free far more effectively than a steady pull.
Mechanical vs. hydraulic action
Jars are broadly mechanical or hydraulic. A mechanical jar trips at a preset load through a latch mechanism, giving a crisp, repeatable release. A hydraulic jar meters fluid to create a time delay so the driller can build tension before it fires. Many BHAs run a jar together with a hydraulic accelerator to maximize impact energy at the stuck point.
Why it matters for rentals
Because a jar may sit idle for an entire trouble-free well yet be critical when needed, renting avoids tying up capital in specialized fishing insurance.
Our BHA components and fishing tools include rental jars; contact us to size a jar and accelerator for your string weight.