Lock Ring, Spindle Nut 

Lock Ring, Spindle Nut
Part Number: 2091
Weight: 0.01 lb

Price: $0.95

In stock
Spindle nut lock ring

In your instruction manual, this part appears on the parts list as:

Item No Models
28  Harbor Freight 47158 Central Machinery Micro Mill
Clarke CMD10 Metalworker Micro Mill
Various X1-US SIEG Micro Mill
Click your model to see the complete parts list.