Downhole anti-rotation tool

A tool to prevent rotation of a downhole tool suspended in a wellbore casing comprising:

• (a) a tubular housing having a bore and having at least one end for connection to the downhole tool;
• and
• (b) a jaw having a hinge and a radial tip, the jaw being pivoted at its hinge from one side of the housing, the jaw's pivot being offset from the jaw's center of gravity so that the jaw is pivotable upon rotation of the tool between a first position stowed against the housing for permitting movement within the casing, and a second position wherein the radial tip swings outwardly from the housing to engage the casing for arresting tool rotation and forcing the housing against the casing opposite the jaw, the jaw having a profile and the tubular housing having a corresponding profile so that when stowed, the jaw only projects minimally from the housing, the jaw further being trapezoidal in shape having sloped top and bottom edges so that the jaw is caused to rotate to the stowed position if contacted with an obstruction in the wellbore during running in and tripping out.