PEPPERLONELY Brand 100 Sets Aluminum Tone Backs Cover Metal Buttons Quantity: 100 Sets Size: 21mmx21mm(7/8"x7/8") 20mmx20mm( 6/8"x 6/8") Hole size: 2.5mmx2mm( 1/8"x 1/8") Thickness: 4mm(1/8") 6mm( 1/8") Material: Aluminum(Cadmium Safe)