cutequeen round ceramic industrial ferrite magnets for hobbies,crafts and science (18x4mm-27pcs, black) cutequeen 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>