Jar 1 : (n) A percussion tool operated manually or hydraulically to deliver a heavy upward or downward blow to fish stuck in the borehole. (v) To apply a heavy blow to the drill stem by use of a jar or bumper sub
US Department of Labor, Occupational Safety & Health Administration (OSHA), Oil and Gas Well Drilling and Servicing eTool, Washington, DC. This is an abridged version of the Dictionary of Petroleum Terms provided by Petex and the University of Texas Austin, USA 2001. http://www.osha.gov/SLTC/etools/oilandgas/glossary _of_terms/glossary_of_terms_a.html, (Oil Well Drilling Sci and Tech - Amer) {492}
