Check the listing for details. 15mm x 4mm Hole 4mm N52 Strong Countersunk Ring Disc Rare Earth Crafts Magnets. Width: 4mm - Hole 4mm, Condition: New. Listed at 13.50 USD. 15mm x 4 mm Hole 4mm N52 Strong Rare Earth Magnet Countersunk Rings Specification:Dimensions: 15mm x 4mm thick Diameter of bore: 4mm Tolerances: ±0.2mm x ±0.2mm Plating/Coating: Ni-Cu-Ni (Nickel) Magnetization Direction: Axial (Poles on Flat Ends) Weight: 4.3 g (0.15oz) Max Operating Temp: 176ºF (80ºC) Pull Force: Approx. 7.2 lb Material Features: N52 Magnets are made of a brittle material. These magnets are not as strong as steel. They are more like a brittle ceramic. If you let two magnets slam together, they can crack and break. This is true for magnets large and small. WARNING!!! Strong magnets should Keep away from Ironware and some easily magnetized iron products, such as monitors, bank cards, computers, televisions, mobile phones and other. These magnets are very powerful which should be handled with great care. Without parents supervised do not allow children to playing magnets as they could get injured. Especially pay attention to the small magnets , please place in somewhere children can't reach place.