Many premade shoe components, such as shoe heels, shanks, and cupsoles, are made in fewer sizes than there are shoe sizes. One component size is therefore reused across a range of contiguous shoe sizes to make a full run. For example, a size 10 heel may be used to build shoes in sizes 9, 9½, 10, and 10½, with the next-largest, size 12 heel covering shoe sizes 11, 11½, 12, and 12½.
The notional steps between sizes of shoe components are called “die breaks”. Accounting for the disproportionate differences in dimensions between component sizes across die breaks is a key requirement of grading for most mass production shoes.
The term “die break” comes from the dies, or forming tools, that stamping and molding processes require for each size of component to be made. Dies are relatively expensive to design, manufacture, and maintain. Their costs creates incentives to reuse fewer component sizes across full runs of shoe sizes.