INDUSTRIAL GRADE: 25 lbs tension of white magnetic hook is based on the direction of tension perpendicular to the contact surface -- reduced by 2/3 if magnet hooks are used horizontally.Please note that the tension of the magnet hook is also affected by the direction, the material of the contact surface and other factors.BEST COATING:Hook magnets are coated with Ni+Cu+Ni Triple Layer. The best coating available, which provides a shiny and rust resistant coated, provides protection for the magnetic hooks for hanging and helps magnetic hooks for classroom to prevent chipping or cracking.MULTI PURPOSE: Magnets with hooks are easy to install and use because of its simple structure.Strong magnetic hooks for hanging are ideal for hanging small objects in places with iron or steel, such as cruise cabins, home, school, workshop, indoor and outdoor.ATTENTION PLEASE: If you want to use these strong magnet hooks on stainless steel refrigerators, we suggest to put a tissue or something else between the magnet hooks for fridge and the surface to protect the surface from scratching.PROFESSIONAL SERVICE We are a magnetic hooks supplier with professional strength. You can certainly find magnetic hooks cruise you want in my shop If you need mass customization of magnet hooks for classroom , contact us and we can meet your needs.