SCOSCHE MPRNDRK-SP MagicPlate Metal Plates Compatible with Original PopSockets Grip for use with Any MagicMount or MagicMount Pro Mount https://www.amazon.com/dp/B079W2B29W/ref=cm_sw_r_cp_apa_i_PyAZCb5VF2TJD
It goes on the back of your popsocket design button.
I use popsockets, so I personally got some popsocket metal plates and use them with a CD slot magnetic mount.