These magnets are intended and tested for use with magnetic trays and GW bases as a point of reference. Of course, you can also use them to magnetize turrets, weapons options, and other modeling shenanigans.
These 3/16" x 3/32" N42 are Flush with small infantry style GW bases, and only about 2/3 of the internal height of the bottom of larger GW bases leaving about 1/3 of a gap in height. When there is a gap, it is highly recommended to use Green Stuff to help hold the magnet in place, as thin super glue (cyanoacrylate) tends to be brittle and the magnets may snap off.