Sinker Bar

The sinker bar was next below the rope socket and screwed into the socket's box by a straight pin having eight threads to the inch (1880) as likewise do the other tools of that period.  The sinker bar of the 1870's was a solid rod 18 feet long, 3 1/2 inches in diameter and weighed about 540 lbs. (or 780 lbs. if the rope socket and upper half of the attached jars are included).  It worked together with the links of the jars to cause a very strong blow on the upstroke to the auger stem below the jars.  The upward blow actually brought about a tug or pick-up of the auger stem and bit.  This greatly helped to prevent the tools (especially the bit) from sticking in the hole.  The sinker bar is not otherwise engaged in drilling the hole.  It is suspended in the hole and thus does not add weight to the auger stem and bit.

Sinker bar shown with tapered pin. Bar lengths were variable in the different oil regions.  Oil Well Supply catalog, 1913.