The round format is optimal for attaching to round things - if you have something in a square shape

Pack of 5 hand-painted rocket magnets from Trendform

A4 blue magnetic foil

You can find data sheet for Hand Lifter 235 Fixed here

and because it's so flat

Power magnet, Blok 10x10x2 mm. 3M The round format is optimalNeodymium magnets Powerful magnets Length: 1 cm Width: 1 cm Height: 0. 2 cm Strength: approx. 1 kg. Flat, square power magnet with incredible strength. This size of power magnet is not suitable for glass boards. SPECIFICATIONS: Strength: approx. 1,000 g. Material: NdFeB Magnetisation: N45 Gauss: 13200 13700 (1. 32 1. 37 T) MGOe: 43 45 Max. temperaturee: 80C Surface: nickel plated (Ni Cu Ni)