Metal sewing machine bobbin. Also due to it's design with many holes they are also very useful for making custom jewellery (I know. Fancy that!)
Height 11.4mm
Diameter - 20.5mm
Inner Diameter - 6.3mm
Sold by the pack. There are 5 bobbins in each pack. 
Don't see your size bobbin? Send us an email with the size you require and we can try to source if for you. Or give us call.