This is a set of 4 weather boot or dust cover for push to reset breakers.  This is used to keep weather and elements away from the button and increasing the life of push to reset breakers in outdoors and conditions in areas such as boats, generators and other applications.  I do have listings for the breakers also in 15, 20, 25, and 30 amp.  (breaker is only for application illustration and is not included in this listing)  The thread size of the captive nut is 12mm x 1.0 thread pitch.