Universal Linkage Pivot System allows easy installation on an excavator arm without removing dipper arm linkage, cutting the installation time. Increased rotation allows the thumb to match the bucket through almost 100 percent of its working cycle. Collapsible linkage design also allows thumb jaw unit to close further, which prevents damage to arm while machine is in transport position. Built-in linkage positional stops offer protection of the cylinder on both the inward and outward stroke. Thumb includes a retaining pin to prevent cylinder drift when not in use.