These are our latest Ring plate sets available in set of 3. Strength varies depending on width of diameter of ring plate. Strength will also vary from smartphone to smartphone case. If smartphone case is too thick then it should be used on outside of case (cases must be completely flat on outside to use). We recommend these to be used the thinner cases on inner part of smartphone case. If used on outside allow 1-2 days to dry before using and apply a lot of pressure against case so it sticks well and permanently. These plates when combined and used with our magnetic smartphone holder (Sold Separately) plates are now extremely strong and can hold an iPad Pro as well. These are plates to be used with round magnetic holders, these are not magnets. If you want full strength and don't use the wireless charging we recommend using the full round plate for best performance but if you use wireless charging we have to open ring sets available as well so you can still use wireless charging.