What are Grade 9 bolts? And where do they come from?
This edition of the Fastener Training Minute with Carmen Vertullo was originally published March 13, 2019 as “What are Grade 9 bolts” during episode 138 of Fully Threaded Radio.
A question came up recently regarding a product we all know as Grade 9, Grade 9 bolts. What are Grade 9 bolts? And where do they come from? And how do we use them or misuse them? And what do you need to know about Grade 9 bolts?
Well, when I first came into this industry, I won’t tell you how long ago that was but it was a while back, we sold a product called F911 bolts. They actually were sold by a company called Porteous fastener Company, but were made by Lake Erie. And they were very popular because they were stronger than Grade 8 bolts. In fact, they were as strong as an alloy steel socket head cap screw. In the inch world the strength of a grade 8 Bolt is 150000 PSI, and the strength of a Socket Head Cap Screw is 180000 PSI in the smaller sizes and 170000 PSI in the larger sizes. The F911 product or Grade 9 was advertised to give you a bolt (actually a Heavy Hex Head Cap Screw) with the same strength as an alloy steel Socket Head Cap Screw, and it was very popular for those applications where higher strength was desired, such as racing car builders. Certain types of heavy equipment folks like them a lot.
If you’ve been in any of my classrooms, you may have heard me speak out against this product because it doesn’t meet any particular fastener specification, and there are lots of different versions or private label brands of them. I don’t think the F911 is been around for a while, but now we have the L9 product and we have the G9 product. I’m not going to necessarily endorse anybody’s name that makes these, but we have the PFC9 product and we have Bowmalloy, and Bowmalloy probably was the original version of this product. Actually BowMalloy advertises up to 200,000 PSI tensile strength. So these are basically higher-strength versions of a Grade 8 bolt and if we were going into the metric world, we would have this product automatically available as a property class 12.9.
It’s one of the reasons you probably heard me say that metric fastener design standards are superior to inch standards in some regards. They are in this is regard because the steel fastener specification for metric product allows for a high-strength property class 12.9, which is the equivalent of 180000 PSI. So we don’t need this Grade 9 product in the metric world, we only need it in the inch world. Now recently ASTM has developed a few higher-strength products. No one’s manufacturing them but there are some specifications available. So here’s my opinion, and maybe this might not be in agreement with everyone, but if you need a product that is higher strength than Grade 8 and the difference between a Grade 8 and a Grade 9 (there’s no such thing as a Grade 9 specification, that’s just what we call them). If the high-strength product is that important to you, you probably ought to be looking a little bit closer at the design; it might be better to just use a larger Grade 8 bolt.
Most of these products come zinc-plated, and any time we zinc plate a product that has a high tensile strength of 180,000 PSI, we have a hydrogen embrittlement risk. Now this is a fairly sophisticated product so manufacturers probably do everything they’re supposed to do to mitigate that risk by properly baking and testing the product. But if you were going to use this in a critical application, and I would assume it would always be a critical application or you would not be concerned about that extra margin of strength, then you would want to make sure that the product was properly processed. So if you’re going to specify this type of high-strength product, then find out from that supplier how these products are plated, how they are baked, How they are tested, to make sure that you don’t incur a hydrogen embrittlement risk.
It’s a very good product. If you’re a fastener supplier, there are good margins. There’s good money to be made. It’s important though, that you also know they generally are sold as a system. You’ll be generally buying the bolts, the nuts, and the washers as an assembly, because for a higher strength bolt, we need a higher strength nut. The standard Grade 8 nut would not be appropriate for this bolt. Well, that’s what I know about the PFC9 , L9, G9 Bowmalloy. If I left your favorite one out, I’m sorry about that. There are multiple different versions of these and if you’re using them, you know how to get hold of me, Carmen at AIM Testing Laboratories. I would love to talk to you about your experience using Grade 9 bolts.