The dipper arm (also called arm or stick) connects the boom with the bucket and is the middle link of the three-part excavator working equipment (boom → arm → bucket). Its length crucially determines the digging and demolition depth as well as the machine's reach.
Standard arms are available in short (for maximum digging force) and long versions (for maximum reach). A Cat 320 has a digging depth ranging from 5.7 to 6.7 meters depending on the arm. For special applications, there are telescopic arms (hydraulically extendable by 1–2 m), longreach arms (up to 12 m for waterway maintenance) and demolition arms with reinforced construction.
The arm absorbs extreme bending loads and is one of the most heavily stressed parts of an excavator. Crack formation at the welds is a common wear pattern, especially in demolition work. Regular visual inspection of the arm welds and bolts is part of the daily operator tasks.