price) will probably never complain that the transmission was not field-serviceable as long as they themselves never had to pay for transmission service in the lifespan of their ownership. This analysis can be important for the manufacturer to understand (even if it is lost on the customer), because he can carve for himself a competitive advantage in the marketplace if he can accurately predict where to "cut corners" in ways that the customer will never have to pay for. Thus he could give himself lower transmission unit cost. However, he must be sure when he does so that the transmissions he's using are reliable, because their replacement, being covered under a long warranty, will be at his expense. Random assembly available but not ideally desirable: "light" and "heavy" parts The other main area of application for selective assembly is in contexts where total interchangeability is in fact achieved, but the "fit and finish" of the final products can be enhanced by minimizing the dimensional mismatch between mating parts. Consider another application similar to the one above with the 12 mm pin. But say that in this example, not only is the precision important (to produce the desired fit), but the accuracy is also important (because the 12 mm pin must interact with something else that will have to be accurately sized at 12 mm). Some of the implications of this example are that the rejection rate cannot be lowered; all parts must fall within tolerance range or be scrapped. So there are no savings to be had from salvaging oversize or undersize parts from scrap, then. However, there is still one bit of value to be had from selective assembly: having all the mated pairs have as close to identical sliding fit as possible (as opposed to some tighter fits and some looser fits—all sliding, but with varying resistance). An example of a product that might benefit from this approach could be a toolroom-grade machine tool, where not only is the accuracy highly important but also the fit and finish. See also Allowance (engineering) Engineering fit Engineering tolerance Fungibility Just-in-time (business) Louis de Tousard Modular design Preferred numbers Configuration management References Bibliography . . . Traces in detail the ideal of interchangeable parts, from its origins in 18th-century France, through the gradual development of its practical application via the armory practice ("American system") of the 19th century, to its apex