Bar Stock - Standard Sizes Throughout A Supply Chain

Standard Sizes Throughout A Supply Chain

To stock every possible size of bar stock (every possible fraction of a millimetre or inch in diameter or thickness) is impossible. Thus, bar stock is stocked by metals supply houses in various standard sizes, arrayed in discrete steps. For example, round bar with diameters of even millimetres (or in the USA, on the eighths of an inch) can usually be ordered from standing stock. Bar diameters of nonstandard sizes can also be obtained, but only as a separate mill run from the rolling mill. Thus they are much more expensive than the standard sizes, can take much longer delivery time, and are not desirable as inventory for the supply house or the machine shop (because the chance of selling or using any particular custom size is slim).

Sometimes it is necessary that the bar not be very much larger than the intended part, because the metallurgical properties of some metal alloys in some finishing processes may vary by how far inside the bar the metal lies. Thus an engineering drawing will specify a certain size (or a maximum size) that the bar may start out as. These specs face the aforementioned limitation of stocking sizes versus custom mill runs; standard sizes are used wherever possible to avoid wasted expense and needless delays.