1) Diameter is 30mm(1.18"),thickness is 5mm(0.196") and 18mm(0.71"),thickness is 4mm(0.157")<br> 2) it is Ferrite Magnets,not strong magnets<br> 3) it is Grade 5. <br> 4) it is highly stablility udner difficultal environment.<br> 5) notice:It is only for science,craft and production use,Not toys.<br> 6) 30 days Unconditional refund.<br>