So now and then this type of characteristic shows up in discussion with your customer. What is it? Well, when a part makes it to your customer and your customer has some kind of trouble with it. With parts getting more complex and are often assembled into sub-assemblies. Your company does not make all the parts that go into the sub-assembly, but the parts are purchased. Some of the purchased parts have features (such threaded holes, pins, clips and in general Form, Fit or Function features) that your company does not check, but are key features for your customer. When one of those features is missing or damaged, your customer has a problem.
In short, pass through characteristics are those characteristics that have potential form, fit or function problems that will not be detected by your company, but will cause problems at your customer or customer's customer.
Think about an engine. When it arrives at a car assembly plant, many connections have to be made (radiator, air, gas, transmission, cables and so on). Many of these features come from parts you have purchased from suppliers. The stud or the clip is a pass through characteristic for you (you do not touch, make it or inspect it) and can create a serious problem for your customer.
You would say inspect it. In some cases that is possible or error proofed, in others it is not. For example it is not easily accessible or very expensive to inspect.
What do you do?
The characteristics must be identified all the way through the quality documents (Design FMEA, Process FMEA, Control plan). You always should inform your customer what the pass through characteristics are.
Key in establishing the pass through characteristics is that they should be developed during the development process (not after start of production). Your supplier should be fully aware and should have special controls in place to prevent defects leaving the suppliers facility.
What if you are already in production?
Review all your customer concerns (not just the official recorded concerns) and see which were form, fit or function issues that your company can not detect. Then take these to your suppliers and find out what how they are controlling these. You might find out that your supplier does not have controls. Here is your starting point.
Differenr approach?
Another approach you can take is to define any form, fit or function (or pierce points or attach points) as a special characteristics (significant characteristic) in your DFMEA and cascade those characteristics down to the supply base. In this case you would not need a pass through characteristics class.
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