MIN CI 40 Pcs Super Strong Neodymium Disc Magnets, 18 mm x 3 mm Small Magnets for Dry Erase Board Whiteboard Office Fridge Crafts, Mini Round Rare Earth Magnet s for Building Scientific Models

I have worked with quite a few ultra-powerful neodymium magnets in the past 3 years, some of which are outright dangerous if handled recklessly, such as strong enough to crush fingers that get in the way, or outright lift refrigerators and small steel engine blocks. This is not one of those kind of magnets, but I still treat all neodymium permanent magnets with respect for safety.This was the perfect size to replace the anemic weak magnet in the antenna for a cellular network access "fail-over" device, so it would stay put on a vehicle or in a portable application in high winds.The original antenna underwent "sudden violent separation" from a car roof, followed by high velocity contact with the highway surface and dragging by its attached coaxial cable, accompanied by multiple secondary impacts with pavement and the side of the car until the driver was able to come to a stop after about 400 feet. Pieces of debris from the antenna base were recovered from the highway, bagged, and taken home to see if there was any hope of repair; not due to the cost - only a $25 antenna - but the 6 to 8 weeks of supply chain delays to acquire a replacement.Following examination of the debris, it was quickly determined that the tiny magnet used in the base during manufacture was woefully inadequate to hold it to the roof of a vehicle at highway speeds.A small mold was made to replicate the shape of the plastic base, the recovered fragments were placed approximately where they would have been before the accident, the metal parts were verified to still have electrical and RF integrity, and a small amount of resin was poured to reconstruct the base.The steel cup in which the original magnet had been placed, was measured for inside bottom diameter, as was its depth with a machinist's gauge. With sufficient cup clearance calculated to maximize magnetic field strength out of the bottom, these magnets were selected and ordered as the best fit and likelihood of sufficient strength to upgrade the base holding force to an acceptable performance level in the field.While the magnets were en route, the antenna system was tested with a rather expensive microwave antenna and feedline analyzer, and determined to be still functional within the cellular 4G spectrum.The empty cup was filled with JB Weld epoxy (which although it contains steel powder and is slightly magnetic, does not divert more than a few percent of magnetic flux). This was used to "pot" the magnet so when removing the modified rebuilt assembly from a car roof, it will stay firmly attached to the antenna and not the car.24 hours later once the epoxy had fully cured, the repaired unit was placed on the car roof, with a camera anchored nearby to observe it. The antenna analyzer was connected to the coax, and set up to monitor impedance and reflected energy in the center of the 4G cellular spectrum, and the unit was taken on a test drive.The first leg consisted of about 2 miles of incredibly rough dirt road, which subjected the unit to extreme vibration, which should induce microscopic very fast separation and gap closure over millisecond intervals, which can cause data errors and "chopping" of voice over IP. The magnet was strong enough no significant signal degradation was observed.The second leg was about 4 miles of secondary road at between 35 and 50 mph. The final leg was 10 miles out and 10 miles back of highway between 75 and 80 mph to observe aerodynamic behavior and the magnet's ability to overcome these forces.The magnet passed with flying colors.Most people won't use them for this, but it worked well. I'm going to put another one in a TV remote so it stays put on a steel cabinet when not in use, and the cats can't hide it under furniture.

Wish they were a little bit stronger. Worked just fine for what i needed them when i doubled them up..

Great little magnets. 60 pcs 6 x 2mm were all in excellent condition. Very strong attraction for their size. I use for 3D print items and their dimensions using my digital caliper are 5.94mm x 1.96mm. Verified my calipers with a precision shim set.

These are good magnets, but their not as strong as I need. And they are very fragile. The first magnet that I separated from the bunch, slammed back into the others and broke.

Very strong magnets. My brother found it difficult to pry them off of one another. They work great for his 3d printed projects

Love the build quality, super strong and magnetic problem is their hard to get off the stack once you can separate them they work wonderfully. Require super strength to remove them because they are sent vertically stacked and the magnet is so strong. They’re trying to get each magnet off, requires gorilla like strength, which is simply reflective of the degree of magnetism they possess.

Nice for a simple, normal magnet task - refrigeration magnets, etc. But I am trying to use for something quite specific. And each time I 'believe' I have found the North on the magnet, because there is apparent repulsion when my two 'believed' Norths are facing each other, and no magnetic pull when the two opposite sides are facing each other... the next day it seems to have been incorrect. Huh?So I'd make adjustments. But over and over this has happened. Yesterday thought this was finalized, only to be disappointed again today.BUT - if using for a REGULAR magnet, they will to stick 'well enough' on both sides to a metal piece. So don't worry - unless you have a particular need or strength in mind.My biggest issue is that I have written twice asking for the Gauss (strength), and no seller response. So one mark down per issue: no North marking, no Gauss mention in description or in response.

Very strong for their size. I only need 1 to hold up multiple pieces of paper on a fridge. One single magnet can also hold a thick photo or laminated sheet, no problem. Better than another, cheaper brand I tried.