Dillon Precision Powder Return EZ Adjustment Nut V3 by Entirely Crimson 

Speed Nut for the failsafe return rod on Dillon Automatic Powder Measures. Easy and fast to install, adjust, and remove with the press of a spring loaded button. To install, align the holes and slide over the threaded end of the return rod. The button presses flush to install or release. The button pops out when locked into the rod threads. Can be twisted to thread up or down for fine adjustment or just press the button flush and slide this speed nut. Works with all Dillon Powder Measure Failsafe Return Rods.

Be sure to adjust the nut properly before actuating the press or you may cause damage. The Powder Measure Return Rod Spring coils should not press flat against each other or it is over tight. 

Version 3 is a round style with all the features of square Version 2. V3 and V2 have a button retaining screw that keeps the assembly together when it is not installed on the return rod. The Silver and Red do not have a button retaining screw.