Retraction Mechanism for threaded nut

[shishir.iitr]

Hi,

I have been trying to find all the retraction mechanisms possible to bring the nut back on the threaded shaft when it comes forward. Constraint is geometry. Between the back of nut and the face of the threaded shaft, space is max. 6 mm. also, the nut moves only 2 mm forward on shaft. Please help.

 

[Baluncore]

You could employ a “half-nut” as used to engage the lead-screw on a thread cutting lathe.
http://en.wikipedia.org/wiki/Split_nut