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Note: The drilling jar which is connected with drill tool and worked with drill string is a downhole stuck freeing tool in drilling operation .It is a first selected tool for directional well,complicated well and deep well.The drilling jar is consisting of drilling up jar and drilling down jar,both they can be used mutually or operated separately .The up jarring section takes use of hydraulic mechanism,the jarring force can be adjusted according to up elevating load but can not exceed the max.load for tool load rated .The down jarring section takes use of mechanical friction mechanism, the jarring force is well preadjusted by adjusting device before put into downhole.No re-adjustment can be allowed after jar is put into downhole.