These magnetic clasps have a hole of approximately 30mm x 2mm or 3mm

They can be used with: 1 piece 30mm flat leather / 1 pc 20mm flat leather + 1 pc 10mm flat leather / 3 pcs 10mm flat leather / 2 pcs 10mm flat leather + 2 pcs 5mm flat leather / 6 pcs 5mm flat leather