FTM 99: Where should I NOT use socket set screws?

An application was using 3/4 x 4 inch socket set screws, and the user was breaking the set screws. Why

This edition of the Fastener Training Minute with Carmen Vertullo was originally published November 19, 2015 as “another war Story about socket set screws” during episode 99 of Fully Threaded Radio.

Hi, everybody, this is Carmen Vertullo with the Fastener Training Minute brought to you by Fastener Training Institute and Carver Consulting.

If you’ve been in one of my classrooms, you will have heard me say that if you ever have a technical question or any kind of question: sales, purchasing, career advice even, send me an email and I will answer it for you.

So I get these questions from time to time, they’re always very informative and interesting, and I call them War Stories. So when we come back we’re going to talk about one of these War Stories that has to do with the use of a socket set screw. You’re going to learn two lessons; one is a technical lesson about set screws, and the other one is a good sales lesson.

One of my students emailed me a question regarding an application with a socket set screw. This was a three-quarter inch by fairly long three or four inch alloy steel socket set screw, and the user was breaking the set screws. And so of course, they thought something was wrong with the set screws and complained to the customer. They sent me a video. I got to see exactly what they were doing.

What they were doing with the set screws were that it was in a structural application where they were screwing them into a blind hole and using them as a stud. They were just going to hang the steel on that stud and put a nut on it and tighten that nut down.

Well, the set screws were breaking, the customer was very frustrated. They had good engineering on this they thought because as you know, socket set screws are very strong. The materials are very hard with that ASTM F912 requirement of 45 to 53 Rockwell C, which is about the hardest threaded fastener that we have.

The problem is whenever fasteners in general, or materials are very hard, they also tend to be brittle. So socket set screws are not meant to be used in tensile applications. And that’s what they were doing with this particular set screw.

Sadly, they sent it out to the lab, wasted a bunch of money trying to figure out if something was wrong with the material when in fact there was nothing wrong with the material. It was simply used in the wrong application. We told the customer this information they were happy to hear it. But of course you never want to just say something to the customer regarding their application problem, you want to give them what I like to call an authoritative citation.

And in this case it came from ASTM F912 or IFI Inch Fastener Handbook 9th Edition. Look up page 506 and it says this in paragraph 1.2these set screws are intended for compression applications only.” So it’s one thing to say “Hey, I heard it on fully threaded radio” but it’s quite another thing to be able to say ASTM F912 says so.

So those are your two lessons, one is that socket set screws are not made for tensile applications. And the other is that whenever you want to give a customer some technical information, always use an authoritative citation. And if it turns out that you have this situation and it involves a metric set screw, you would go to ISO 898-5 Annex A which says “the use of set screws of hardness of this class under tensile stress is not recommended.

Thanks for listening. This is been Carmen Vertullo with the Fastener Training Minute.

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