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DIN and ISO standard parts, and when a special is cheaper
A standard part is cheaper until the standard does not fit, at which point a special is cheaper than an assembly designed around a compromise.
Standard parts to DIN and ISO are cheaper because they are made in volume against a published specification that every supplier can read. Where one fits, use it: the cost, availability and second-source position are all better.
The mistake is designing an assembly around a standard part that nearly fits. A washer stack to take up a length difference, or a machined recess to accept a head that is slightly too large, costs more over a production run than a non-standard part made correctly once.
Most of our orders contain both: catalogue fasteners for the ordinary positions and a handful of specials that exist in no catalogue. Keeping them with one supplier means one lead time and one person to chase rather than two of each.
Specifications
| Use a standard when | It fits without designing around it |
|---|---|
| Use a special when | The workaround costs more over the run |
| Typical order | Catalogue fasteners plus a handful of specials |
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A grade that machines more easily may corrode sooner, and that trade-off belongs to the buyer rather than the supplier.
What a drawing needs to carry for a firm quote
Material grade, quantity, critical features, finish and any standard reference, plus a sample where one exists.
Have a drawing ready
Send the drawing with the material, the quantity and the finish you need. You will get a price, a process and a lead time, and a free sample before volume production.