A split nut is a nut that is split lengthwise into two pieces (opposed halves) so that its female thread may be opened and closed over the male thread of a bolt or leadscrew.
It is one of the machine elements that makes single-point threading practical on manual (non-CNC) lathes.
The two halves of the nut have chamfered ends (60° to the axis), which helps the threads to find engagement during the closing action.
Such provisions prolong the service life of the threads by minimizing wear.
[2] Split nuts may not engage and disengage with multi start threads due to the overlapping leads.