Bests & Worsts Reviews from Amazon

(The 22 lb magnetic hooks I bought are no longer listed in the ad. They are now selling 25 lb hooks instead. Just something to keep in mind when reading calculations based on the 22 lb hooks I bought & reviewed below.) *************************************************************************** Among other things, I'm using these on three steel doors to hold the curtain rods that hold the curtains. They are quite strong for their size (base is 1/2" in diameter), and I'm very happy with their (parallel) holding power. I docked one star for two hooks that don't fit in their base, demoting them to refrigerator magnets. Simply put, a magnet's PULL STRENGTH measures (in kilograms or pounds) the amount of VERTICAL force required to PULL the magnet AWAY from the metal surface it is stuck to. Applying that to these magnetic hooks means that each one, when stuck to a metal CEILING, is rated for a maximum holding power of approximately 22 lbs/10 kg before it will PULL AWAY from the CEILING. (Assuming all CONDITIONS ARE IDEAL.) Take the same magnetic hook and put it on a WALL made of exactly the same material as the ceiling, and it will SLIDE DOWN the wall much easier than it will PULL AWAY from the ceiling (or PULL AWAY from the wall, for that matter). This is the magnet's PARALLEL HOLD or SHEAR FORCE, and it's not nearly as powerful as its PULL STRENGTH. This same concept explains why 2 magnets stuck together are easier to separate if you SLIDE them apart than if you try to PULL them apart. Manufacturers are generally referring to PULL STRENGTH when stating the holding power of a magnet. Pull Strength is determined by the MAXIMUM AMOUNT OF WEIGHT A MAGNET HELD WHEN TESTED UNDER IDEAL CONDITIONS. PARALLEL HOLD/SHEAR FORCE can be reasonably estimated at 10% to 25% of a magnet's PULL STRENGTH. With that in mind, we'll assume a PARALLEL HOLD of 17% for these magnetic hooks rated at 22 lbs (22lbs X 17% = 3.74 lbs). Under that assumption, we can expect that each hook (if used on a metal WALL or DOOR) should hold approximately 3 3/4 lbs of weight before it SLIDES DOWN THE WALL. Obviously, that's much less than its stated pull strength of 22 lbs (the amount of weight it should hold if used on a ceiling). Because a magnet fails under less weight when used on a wall rather than a ceiling, or holds less weight than stated on packaging or sale ads, does NOT mean that the magnet is flawed or the manufactuer and sellers are deceitful. The magnet is simply demonstrating, in real life, (and perhaps to the user's dismay), the difference between its PULL STRENGTH (22 lbs in this case) vs its PARALLEL HOLD/Shear Force (approximately 2 1/4 to 5 1/2 lbs = 10% to 25% of 22 lbs). In addition to orientation, there are other factors or conditions that influence a magnet's performance/strength/holding power, SUCH AS: THE MAGNET: **What is the magnet made of, what type of material? (ceramic, alloy, rare earth, etc), **What is the magnet's CONDITION? (chipped, cracked, scratched, dirty, etc) **What is its size and shape? **Is the magnet "CUPPED" or not? Cupped=magnet is placed into a steel 'cup' or 'holder', like the magnets on these hooks. Cupping 'focuses' most of the magnet's pull in one direction [the open end of the cup], giving it more holding strength than it would have without the cup. **How has the magnet been HANDLED? Has it been stored correctly (it matters)? Has it been dropped? (dropping magnet=not good) ENVIRONMENTAL: **What is the AMBIENT temperature and humidity level? Is there excess moisture present? **Will the magnet be completely submerged, used to attract submerged items? **What is the temperature of the metal the magnet will attach to? - What is the temperature of the magnet? THE METAL: **What of the metal the magnet attracts or attaches to? - How thick is the metal? (thicker = better) - What are its components? **What is the condition of the metal item or surface? Is it BARE and CLEAN or is it coated, painted, dirty, greasy, rusty? - Is it perfectly FLAT or is it curved or uneven? Is it perfectly SMOOTH or is it textured, rough, bumpy, dented, chipped? ANYTHING THAT INTERFERES WITH 100% FULL & DIRECT CONTACT BETWEEN MAGNET AND METAL DIMINISHES THE MAGNET'S HOLDING POWER. ~~~and that's just the short list, there's more, and it ALL matters. I think the physics of magnets and magnetism is fascinating, but technical and complex enough to blow MY mind right out of the science book! Fortunately, for most of us 'average consumers', this very BASIC understanding of PULL STRENGTH as it relates to PARALLEL HOLD is likely the most beneficial (and easiest to remember) when choosing a household, craft, hobby or shop magnet for your particular task. ********************************************************************************* NOTE: IDEAL CONDITIONS for testing a magnet's holding power means the METAL is thick, perfectly smooth and flat, perfectly clean and bare. Same for the MAGNET, it is in PERFECT, new condition. Ambient conditions [temp, humidity, dust-free, etc] are also PERFECT. Everything is as perfect as it can be in order to achieve the maximum holding power of the magnet, and that result is what is stated on packaging, in ads, etc. Our personal-use conditions are not likely to be as perfect as testing conditions.