China Neodymium And Ferrite Magnets Manufacturer & Supplier 
Have you noticed that there are very few sintered ferrite magnets with countersunk holes? Essentially, all magnets with countersunk holes are made of neodymium-iron-boron. Why is this? Is it because they cannot be machined?
To answer your question straight away, it is mainly because ferrite is difficult to machine further; furthermore, its magnetic strength is weak; and, more importantly, machining countersunk holes significantly increases the cost.
Magnets with countersunk holes are typically used in conjunction with screws for fastening, for example, when mounted on equipment casings, display stands or door stops. The magnetic energy product of ferrite is typically only about one-tenth that of neodymium-iron-boron. Countersinking further reduces the magnet’s effective volume, causing the magnetic strength to decrease even further. If the magnetic strength is already low, removing a portion of the material often results in holding power that fails to meet application requirements. Therefore, in scenarios requiring countersunk installation, most customers opt directly for countersunk neodymium-iron-boron magnets.
lowered type disc magnet
This negates the advantages of machining countersinks into ferrite magnets. Why is this? Most customers choose ferrite primarily because of its low price; for example, a standard ferrite disc may cost only a few fen to a few mao. However, if a countersinking process is added, the machining costs may even exceed the value of the magnet itself, making it uneconomical.
This is the main reason why recessed designs are rarely used for ferrite magnets. Although they are uncommon on the market, this does not mean that countersunk holes cannot be produced; square, circular and rectangular ferrite magnets can all be manufactured with countersunk holes.
Related ferrite countersunk magnets:
Round ferrite with a square hole in the middle axial 2 poles
20mm thick ferrite magnet with mounting hole OD 80mm
Rectangular ferrite magnet with countersunk hole 25x20x5mm
Rectangular ferrite magnet with 2 countersunk holes in stock