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Below is a cut and paste from ye old interweb. Same holds true for tapping screw or actual using a tap. Some screws are a bit of a combo of taping and forming. You can easily tell those because they get larger diameter after the cutting area. Doesn't really matter though because what's done is done, but comments need to be factual.
Differences Between Form Tapping and Thread Cutting Screws
A tapping screw is a screw that creates its own hole when it is driven into a material, rather than needing to be driven into a pre-drilled hole. There are two basic types of tapping screws, thread forming and thread cutting.
The primary difference between thread forming and thread cutting screws is how the holes are made.
Thread cutting screws have cutting edges and chip cavities that actually cut into the material, removing the material from the part they are driven into.
Thread forming screws do not actually remove any material, but rather they displace it, or push it aside so that the material flows around the screw’s threads.
In general, because they do not require the use of nuts and only need to allow for access from one side of the material, thread tapping screws permit rapid insertion and so contribute to increased productivity
Thread Forming
Thread forming, also known as cold forming, is typically used when larger stresses are needed. This method will stand up to better loosening because no material is removed, creating a fit with zero clearance. Thread forming screws are generally able to stand up against loosening without the needs for lock washers or other devices designed to prevent loosening.
Thread forming is typically used for steels, stainless steels, light metals and light metal alloys. Generally, materials that produce a continuous chip when drilling are good candidates for thread forming.
Thread Cutting
Since thread cutting screws have edges designed to help them penetrate the material, they require less force for insertion, making them ideal for use in materials where disruptive stresses are not wanted or when using thread-forming screws would require too much torque.
Thread forming is believed to provide multiple advantages, including cutting time and increasing strength and durability. Since the material is cold worked, the threads produced are typically stronger and taps can be operated at higher speeds than available for thread cutting. Thread forming also provides for better size control, while improving tool life and productivity.
Here is a boxlink screw. Clearly a thread forming screw.
Another cut and paste from the ol interweb on thread forming taps vs cutting taps.
It is universally accepted that formed threads are stronger than cut threads. When threads are formed, the grain of the material is compressed, particularly at the root and crest of the thread form. While a cut material’s grain structure has been “fractured” by the cutting action of the tool.
Forming taps are limited in use to those materials malleable enough for the process, like non-ferrous metals, aluminum, and soft steel. They also produce a thread-form that is slightly different in appearance when compared to thread produced by a cutting tool.
This type of tap is also a likely solution to the challenges of tapping “blind” holes: as forming taps produce no chips, creating no issues with chip interference and removal.
Last edited by mikeinatlanta; Feb 21, 2020 at 09:40 PM.
Working in the design and construction of heavy oilfield equipment for 41 years before retiring, I can tell you that we would never use self-tapping or self-forming screws to hold anything, even a license plate. Rolled threads are made in a factory, not by self-tapping screw, and typically are only available on high performance cap screws from such OEs as SPS Unbrako and ARP.
Working in the design and construction of heavy oilfield equipment for 41 years before retiring, I can tell you that we would never use self-tapping or self-forming screws to hold anything, even a license plate. Rolled threads are made in a factory, not by self-tapping screw, and typically are only available on high performance cap screws from such OEs as SPS Unbrako and ARP.
Interesting comment when the treads in question are not "rolled", they are formed. While you are of course free to not use better technology, it would seem that others largely disagree as thread forming taps are widely available at pretty much any industrial supply house. They work quite nicely on mild steel and produce superior threads. Thread forming screws are typically 100 ksi or higher. Manufacturers like Ford and John Deere use them, but it's impressive that you guys were able to design heavy equipment and never need blind fastening capability.
Yes, we did design to avoid blind threaded holes. They cause maintenance problems, specially when field repairs are necessary in dirty environments. Too easy for damaged threads to not be properly repaired in the field as finishing taps are not commonly carried by field mechanics. Even fluid in the bottom of the hole can prevent the fastener from being fully seated and properly torqued, especially if a thread compound such as Luctite needs to be used.
Really good information on threads and threading posted here. There is a lot of knowledge on this board. And I appreciate that.
Even in light of the information posted I still think for me, I was better off tapping the holes first. I have horrible luck with such things. I would bet the two holes I had trouble tapping would have been the ones that snapped had I not pre-rapped. But maybe not.
My XL didn’t come with the Boxlink system but I’m adding it.
I know the screws that come with the brackets are self tapping but I’d feel better tapping them first. I got my bed LineXed and with my luck that will be just enough to snap one or more of the screws.
If no one knows that’s ok, I can take the bolts to the hardware store and size them. I’d just like to have the taps ready when the brackets get here.
Thanks.
Has anyone ever answered what size the self tapping screws are?
I was never able to get my OEM cleats into the OEM Boxlink Plates after I mounted them in my Linex'd bed. But I have a few E-trac fittings that work fine. I might grind the bacl of a cleat to see if that helps, but I'm sure it will not be as robust with material removed.
