An illustrative gripping accessory or thumb is adapted for use with a machine having a tool, for example, a backhoe bucket attached to an extendable or non-extendable arm of a dipper stick. The accessory or thumb can be releasably attached to the machine and includes a pair of grip members that can be pivotably coupled to the distal pivot pin connecting the bucket and extendable arm and a grip linkage coupled between each grip member and the intermediate pivot coupling the extendable arm and the rotatable linkage coupled to the bucket rotation cylinder. Thus the use of the gripping accessory with a bucket requires no welding or other permanent modification of the machine and can be stowed or removed when not in use.