FTM 108: What to do with Nicked Threads

This edition of the Fastener Training Minute with Carmen Vertullo was originally published September 22, 2016 as “What to do with nicked threads” during episode 108 of Fully Threaded Radio.

Well, hi everybody, this is Carmen Vertullo with the Fastener Training Minute coming to from the Carver FACT Center in El Cajon, that’s Fastener Applications Consulting and Training, and the Fastener Training Institute. Today’s topic is both technical and practical, one of those issues that comes up frequently that has a very simple solution, and it’s called nicked threads.

So from time to time you have a customer who complains they’ve got nicks on the bolts that you sent them, and they can’t get the bolts to pass the ring gauge test. What do you do?

Today we’re going to give you a tool to help you deal with nicked threads. So the scenario goes like this: you ship some product to a customer, the customer is inspecting the product, and one of the things that they’re finding out during their inspection is that they are dealing with nicked threads. They cannot get the ring gauge to go on the bolt. While we have respect for that, believe it or not many solutions in industry are specification based, in this is one of them.

When the ring gauge will not go on the bolt we use ASTM F788 or F788M or ISO 6157-3. These are all very similar a specifications and they basically say if you’ve got a nick on the thread of a fastener, and it will not go through the Ring Gauge, we’re going to give you a little bit of help by allowing you to apply some torque. How much torque? There’s a very simple formula to determine the amount of torque you’re allowed to use to overcome problems with nicked threads. That torque is equal to 145 times the diameter cubed (cubed means diameter to the 3rd power, or diameter X diameter X diameter).

So for example with a quarter inch bolt, we’re allowed to use two and a half inch pounds of torque to overcome the nicked threads. That doesn’t sound like much but for a quarter inch bolt, it’s a lot. If we get up to a larger bolt, which is where we really have these problems, three quarters of an inch and above, we can use 5.1 foot pounds of torque. If we for example had a M18 bolt we could use 8 Newton meters.

So it’s not a difficult problem to solve. It’s not a difficult problem to address. It’s not highly technical. If you need the reference, and I always like my clients or my students to use authoritative references when they have to cite the solution, in this case, it’s ASTM F788 which is in your Industrial Fasteners Institute (IFI) 9th Edition inch Fastener Handbook.

Well, thank you for listening. This has been Carmen Vertullo with the Fastener Training Minute.

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