FTM 96: The sample size of inspections

Fastener Training Minute 96: The sample size of inspections

This edition of the Fastener Training Minute with Carmen Vertullo was originally published August 20, 2015 as “The Wedge Tensile Test” during episode 96 of Fully Threaded Radio.

Hi everybody, this is Carmen Vertullo with the Fastener Training Institute and Carver Consulting bringing you the Fastener Training Minute. I’ve had a couple of inquiries from my clients and others regarding the sample size of inspections. What is a supplier to do when they receive product at their dock and it needs to be inspected. How do they know how many parts to inspect?

While there are some specifications and standards that help us with this, some of them can actually save you a lot of money if you know how to read them, right? And that’s what we’re going to talk about when we come back.

Quality assurance issues are one of the most important things that fastener suppliers and distributors in particular deal with. I just want to bring to your attention a class on Quality Assurance for Fasteners that we have coming up in the Fastener Training Institute, part of our CFS program in the beginning of September. John Walkman will tell you more about that later if he hasn’t already.

So what do you do as a supplier when you receive a lot of fasteners on your dock and you need to inspect them? Or worse, maybe you’ve never inspected anything and all of a sudden it’s come to your attention that you ought to be looking at your stuff a little bit more closely. Well there a couple of things that you can do. And there a lot of low-hanging fruit available for the faster distributor when it comes to deciding what to inspect.

First thing of course is you’re going to need a little bit of training. So send some folks to the Fastener Training Institute’s classes so they can learn how to inspect fasteners. You don’t necessarily need to be taking the caliper or a optical comparator micrometer all these products, one of the simplest things that you can do to prevent the largest category of rejections from occurring is to simply inspect the product to be sure it is what it’s supposed to be. All you need to do that is use one of those plastic “dummy sticks”, though they are not really dumb and they’re not for dummies, but we call him dummy sticks because they don’t really have any measuring capability. They just identify the parts. You’ve all seen these it’s a plastic device. It’s got some holes in it and it’s got some stuff sticking out and you can use that to identify the part because most rejections aren’t because the fastener is wrong, it’s because it’s the wrong Fastener.

So especially if you are sending product out to the plater to be modified or you just want to make sure that the product is received properly. That’s a good starting point: simply check the stuff when it comes in the door make sure it’s what it’s supposed to be. So beyond that, if you are deciding that you need to do some more formal inspections using some actual instruments such as calipers and micrometers or an optical comparator, what do you inspect?

We have a very good specification that tells us how to do that and it’s called ASME B18.18, and it tells us what our sample inspection size should be based on our lot size. A lot of suppliers misunderstand this specification and they end up using the same requirement that a manufacturer would use, and they inspect too many parts.

So here’s the money page from ASME B18.18 and it’s called Category 1 Optional Receiving Inspection Plan for Purchasers. And it says this:

Category 1 is an optional receiving inspection plan for purchasers. This category utilizes a sampling plan that is not statistically based and focuses on attributes which affect form fit and function for the typical user. Purchasers may use this plan as a basis for determining product acceptability.

The bottom line though says this in paragraph 3.4 Sample Size:

a minimum of eight sample pieces regardless of lot size may be inspected for each applicable dimensional characteristic.

Now this is important because when distributors use the section that is meant for manufacturers, they typically end up way over-inspecting the parts. Those inspections are meant for the manufacturer who actually has control over the production process. The distributor doesn’t have such control and that’s why the smaller sample size is more appropriate.

So first off if you’re not inspecting anything, get started on it. And secondly if you’re doing a lot of inspections and you’re using ASME B18.18 and you are a supplier, bring that sample size down to Category 1.

This is Carmen Vertullo with the Fastener Training Minute and with the Fastener Training Institute and Carver Consulting.

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