Jarring tool with micro adjustment

A latch for a downhole jarring tool, comprising:

• a retainer defining a restrictive region and an open region therein, the retainer having cooperating first and second pieces whereby the restrictive region is axially adjustable by moving the first and second pieces relative to one another;
• an outer latch piece;
• and
• an inner latch piece that is biased against movement through the retainer;
• wherein the retainer retains the inner and outer latch pieces in a latched configuration in the restrictive region and allows the inner and outer latch pieces to unlatch when tensile forces applied to the outer latch piece move the latch pieces into the open region;
• and
• wherein the first and second retainer pieces are in an adjustable fixed relationship such that the first and second pieces remain fixed during unlatching of the inner and outer latch pieces and are manually adjustable relative to one another to move the restrictive region.

A jarring tool comprising:

• a lower sub housing;
• a center sub housing;
• an upper sub housing;
• an upper connector attaching the upper and center sub housings;
• a lower connector attaching the lower and center sub housings;
• a lower stop fitted into a bottom of the lower sub housing;
• a lower shaft fitted through the lower stop and attached to a lower sub end, the lower shaft providing a shoulder inside the lower sub housing for contacting the lower stop when extended from the lower sub housing;
• an outer latch piece attached to the lower shaft inside the lower sub housing;
• an upper shaft passing through an upper stop in the upper connector and having a lower end attached to an inner latch piece and an upper end attached to a cap;
• a spring washer stack arranged concentrically around the upper shaft between the cap and the upper stop;
• and
• a retainer in the lower sub housing having a restraining region;
• wherein the inner and outer latch pieces are restrained by the restraining region in a latched position until displaced through the restraining region due to a tensile force on the upper sub housing and lower sub end;
• and
• wherein the restraining region is in a fixed relationship with the lower sub housing, the fixed relationship being adjustable by rotation of the restraining region about a central axis of the jarring tool.