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These terms in some instances seem to be conflated, or have very similar definitions. For instance, here's a quote from ScrewFix's website on their 'self-tapping and driving screws page' (emphasis mine):

Self-tapping screws are designed to tap their own hole in the desired material, meaning that no pilot holes needs to be drilled before hand.

They make no mention of self-drilling, leading me to believe the two terms are synonymous. On the other hand, ToolStation assures me they are not the same:

Tapping is when screws create threads in the material they are driven into. Whereas regular screws are typically driven into specially prepared drill holes, a self-tapping screw makes its own threads as it enters. However, they still require a pre-drilled pilot hole...

Self-Tapping Screws vs Self Drilling Screws... The main difference is that self-drilling screws do not need a pilot hole

These are both large UK-based trade stores, so I don't think this just a difference in UK/US terminology.

So, what is the difference between self-tapping and self-drilling? And what does "tapping their own threads" mean?

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  • Self-drilling is pretty unequivocal but 'driving' can be misinterpreted (or variously-interpreted if one prefers) which undermines the utility of the term self-driving.... which goes some way towards explaining why there are only 10k returns for that as opposed to 2 mil for self-tapping). Is it supposed to mean the screw pulls itself into the wood? If it is that's stupid, because ALL screws do that! Self-tapping is unequivocal too, but again meaningless in a woodworking context since any screw will create threads regardless of whether it's driven directly into the wood or enters a pilot hole.
    – Graphus
    Feb 27, 2023 at 0:11
  • A more general thing in terms of the sources of the quotes, I made a similar point to this previously re. a quote from B&Q I think it was. No site like Toolstation or ScrewFix should ever be considered a reliable or authoritative source, since the origin of any text is frequently unknown, or could simply be a cut-and-paste of supplied blurb from a manufacturer (which are notorious for being the creation of copywriters, with all the authority that implies).
    – Graphus
    Feb 27, 2023 at 0:17
  • I think I inadvertently invented the term "self-driving", I meant "self-drilling". Maybe one day we'll have screws that can drive themselves into the material... Feb 27, 2023 at 0:32
  • The term "self-driving screw" did already exist although (I think rightly) it's not particularly common. Terminology is what it is though, and meanings can shift for no good reason. It is even possible for one term to gain ground over another and eventually come to dominate — in a woodworking context over the last 10 years or so this has happened with splines taking over from keys (describing the same mitre reinforcement) + over a longer period Moxon vice/vise now completely dominates over twin-screw vice/vise although here the influence could probably be traced, back to Christopher Schwarz!
    – Graphus
    Feb 27, 2023 at 10:25

1 Answer 1

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So, what is the difference between self-tapping an self-drilling? And what does "tapping their own threads" mean?

If you think about the process of preparing a material for a screw the terms may be clearer.
enter image description here
For a screw like this you would have to:

  1. Drill a hole
  2. Tap the hole
    And then it would be ready to use.
  • Self-drilling screws drill their own pilot hole. They have a sort of drill bit built into the tip of the screw which drills a hole and then they create their own threads.

  • Self-tapping screws require a pilot hole to be drilled. When driven into the material they create their own threads.

  • Self-piercing screws don't need a pilot hole. When driven into the material they create their own threads.

Chart
enter image description here

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  • 1
    Re. self-tapping, this is a great illustration of how careful one has to be about which sources to trust or rely on, since this isn't at all how numerous manufacturers of "self-tapping screw" define them — in a woodworking context many (most?) are intended not to need a pilot hole, this in fact being the very reason one would choose to use a them in the first place, e.g. over conventional lag screws.
    – Graphus
    Feb 27, 2023 at 16:46
  • 1
    It may also be important to distinguish between machine screws with their known, and specified, threading and, well, any other kind of screw (where the threading is what it is, and is often not even described much less defined). Although there is now lots of overlap, the use cases for the two kinds of screws can be quite different; and nothing specifically written for metalwork really has any bearing on woodworking applications — where pilot hole sizes are not the same and, most importantly, where pre-threading holes is rare to say the least.
    – Graphus
    Feb 27, 2023 at 16:54
  • @Graphus I think you are right, sometimes a self tapping screw does not need a pilot hole and sometimes it does. In my experience it's often the type of wood I'm trying to drive a screw into that determines if I need a pilot hole or not. For example, I can use a dry wall screw in pine with no pilot but often need a pilot for maple. An example of variation in naming is Kreg screws. They have a drill function but call it self tapping.
    – David D
    Feb 27, 2023 at 19:30
  • All wood screws are "self-tapping".
    – gnicko
    Mar 2, 2023 at 21:12

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