There is a practical size limit to how big the adhesive backed magnets can be. This is because bigger magnets provide magnetic pull forces which will exceed the forces given by the adhesive to stick the magnets in place – the result would be that the force required to take the magnet away from another magnet or ferromagnetic material will exceed the adhesive strength and the adhesive strip will fail and rip off. This is why adhesive backed magnets are small because it keeps the magnetic pull forces to a low enough value.
In applications such as making folders and books with closure magnets, the magnets may be stuck on to the material on the folder or book cover and then the material they are stuck onto is folded over (effectively hiding the magnets from view) such that the magnets clamp together but with the adhesive sides facing (albeit with the adhesive layers plus material layers in between the magnets). This design hides the magnets, allows the magnets to work (perhaps with a lesser clamping force because the magnets are further apart) and clamping and prevents damage to the adhesive backing strip.
The magnets are supplied in stock sizes varying from 6mm to 15mm in diameter and 1 mm to 2mm in height. The stock sizes are axially magnetised and supplied with +/-0.1mm tolerances. The magnets exist in two versions per size – the A version has a North Pole face visible; the B version has a South Pole face visible (so the A and B versions will stick to each other visible face to visible face or adhesive backed face to adhesive backed face). Either version will attract to a ferromagnetic (e.g. mild steel) material.
