This edition of the Fastener Training Minute with Carmen Vertullo was originally published November 21, 2020 as “if you don’t have the point you’re going to get the point” during episode 158 of Fully Threaded Radio.
Hello everyone. This is Carmen Vertullo with your Fastener Training Minute coming to you from the Fastener Training Institute and AIM Testing Laboratory in beautiful El Cajon, California. And it is beautiful here today.
I’m not going to tell you what’s going on right now, but this is a pretty historical time we’re living in and there’s a lot of points being made out there right now, but I’m going to tell you about a different kind of point. This is a kind of point that we find on the end of a screw or bolt and it’s not a very pointy point, but it is a point and the point has a point. And if you don’t have the point you’re going to get the point. So when I come back, I’m going to tell you why the point on the end of a screw or bolt is very important.
A point is a feature that we find on the end of hex cap screws and other types of externally threaded fasteners. It has a very specific requirement and it serves a very important function. Imagine an externally threaded fastener, a bolt or screw. When you look at the end of it, it usually has what you would like to describe as a chamfer and that is the correct terminology: a chamfer. The standards refer to this chamfer as a point and if we were to look at one of the more common standards for hex cap screws, ASME B18.2.1 for example, it has a very specific requirement for that point.
And the reason is because if there is no point on the end of the bolt or the end of the screw, what could easily happen is the last thread on the end of the screw, just wipes out to almost nothing. It can be almost as sharp as a razor blade and that point is very vulnerable to damage. Therefore if that last thread gets dinged or bent it won’t take the nut, and so if we put a little chamfer on the end of the bolt or screw, we keep that from happening. As a matter of fact, bolts are not required to have a point but screws are. Especially with large bolts over half an inch, but even down to a quarter of an inch, if they bang around in a package or get dropped on that thread it will bend.
This is what ASME B18.2.1 says about points in paragraph 2.4. I guess more correctly called the section 2.4.
“Unless otherwise specified bolts need not be pointed.” (So no points for bolts), “Products designated as screws with the exception of lag screws” (we know what a lag screw is, it has a very pointy point), “are required to have a chamfered point.” IFI note: chamfered point lengths should be not less than one but not more than two thread pitches from the end of the screw. The point diameter at the extreme end of the screw should be no greater than the minimum minor diameter of the screw’s thread. Now, that’s not part of the standard, that’s just an IFI note because I am reading this from the IFI version of the standard. It goes on to say “the chamfer angle may vary depending on the manufacturing process. When specified the chamfer angle should be considered a reference dimension only. The presence of a point is to reduce the possibility of damage to the leading threads and promote the ease of assembly with a tapped hole or nut. Point features not defined in a given product standard are at the discretion of the manufacturer.
Now if you were to look at a manufacturing process for cold formed part such as a hex cap screw. You would see this progression as it goes through and at one point in the process, there’s a very subtle change, that is all the sudden before it goes to thread rolling, after it’s been headed, after it’s been extruded, after it’s been maybe trimmed, (I don’t know trim maybe comes after pointing, I don’t know but it’s somewhere in the process) that there’s a point put on the end of the screw. That’s generally done with the material removal process such as some kind of a machining or grinding. It could be done with forming but it’s generally done with a material removal process, and also it is more friendly to the thread rolling process.
So if we look at other inch standards, ASME B18.3 for socket screws, it has a very similar call out to this requirement. It’s not exactly the same but it’s very similar. However, as we know, socket screws start at a very small size, so one of the get-out-of-jail-free cards that can get us into trouble is that as Note 8 from table one will tell us, it’s got very similar stuff to what we just read except it gives us the requirement that for screw sizes up to and including #8, the chamfer is optional. So below size #8, you don’t have to have the chamfer or what they call the point, and we have had issues with that in the past.
What brings this up for me is that we recently had a client who made a bucketload, a large bucketload of long 3/8-24 socket head cap screws. They were 8 or 10 inches long and they sent them to us. We tested and they were fine, they sent them to the plater got them back, and got them to the customer. The customer rejected them because some of them would not take a nut. So they sent them to us and said “Inspect these Threads”. We inspected the threads and the threads were fine. However, we did notice that there was no point, and some of the leading threads were damaged. So that was the issue there. Fortunately those screws probably can be repaired. They are long expensive screws and it will be a hand operation to grind that point on, but we always want to have the point.
I’m going to just go to two more places. ASME B18.2.6 structural bolting also requires a point. It’s a much more defined point and a larger deeper point than other bolting, and you would expect that because structural bolts are kind of used in clunky, heavy rough applications.
Then finally if we go into our ISO or metric standards, if we look at for example, ISO 4762 for the socket head cap screws, it goes to another whole standard called ISO 4753 which has the list of all kinds of points in it. In ISO 4753 it says we should use a point called a chamfered point for sizes above M4. For M4 and below we can use as rolled, which means essentially no point. So again the small screws in the ISO system don’t require points, above M4 does and their specific requirements are in ISO 4753.
Well, I hope you got the point of this point. It’s very important that threaded fasteners have a point because without a point you got no point. Well, this has been Carmen Vertullo with the Fastener Training Minute. Thanks for listening.