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What are these screws called?
What are these screws called?
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Old 13th September 2020, 03:56 AM   #1
K-amps is offline K-amps  United States
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Default What are these screws called?

What are these screws called and where can I get them? They are used in securing output transistors on heatsinks. They seem much more user friendly than the machine screws i have been using. Those need to be tapped, which sometimes ruins the sink plus takes a long time, These on the other hand are just drill and screw types, no need to tap them ... I know they are self tapping, but what kind or where can I order them?
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Old 13th September 2020, 04:05 AM   #2
rayma is offline rayma  United States
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Sheet metal screw. You drill a hole somewhat less in diameter than the screw, and it cuts threads as you turn it.
https://www.homedepot.com/p/Everbilt...0162/204275035

Pilot-hole sizes:
size-4, 3/32 inches
size 6, 7/64 inches
size 8, 1/8 inches

Last edited by rayma; 13th September 2020 at 04:12 AM.
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Old 13th September 2020, 05:17 AM   #3
K-amps is offline K-amps  United States
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Quote:
Originally Posted by rayma View Post
Sheet metal screw. You drill a hole somewhat less in diameter than the screw, and it cuts threads as you turn it.
https://www.homedepot.com/p/Everbilt...0162/204275035
Not the same kind. The ones I photographed have larger threads, and are slotted. They are not home depot types.
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Old 13th September 2020, 06:03 AM   #4
Vovk Z is offline Vovk Z  Ukraine
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I guess they are possibly self drilling sheet metal screws?
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Old 13th September 2020, 06:39 AM   #5
simon7000 is offline simon7000  United States
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Self tapping screws.

Self-tapping screw - Wikipedia
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Old 13th September 2020, 07:10 AM   #6
leadbelly is offline leadbelly  Canada
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What’s the Difference Between Self-Drilling and Self-Tapping?
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Old 13th September 2020, 09:47 AM   #7
JMFahey is offline JMFahey  Argentina
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All "sheet metal" screws are "self tapping" to a point because they are not constant diameter like a "mechanical screw" or "bolt" or plain "screw" intended for a pre threaded hole or nut, instead nthet "startb thinner" so they can oush metal/plastic/wood apatrt.

Easier to do on sheet metal because of not much metal being involved, so itīs relatively easy to push it aside and forming a coarse thread.

Now if sheet metal is thicker or material is not easy to push aside (it can crack) then, as in your example, tip is less "conical" but a slot is ground, so a sharp edge is formed, it can *cut* the base material instad of simply shoving it aside, now your self tapping screw becomes "self threading self tapping screw", it actually works like a built in screw tap.

These are called self tapping screws but they only work on sheet metal or relatively soft plastic (or wood):

Click the image to open in full size.

In my book *these* are the real/full self tapping screws, notice they are way less "conical" (although always there is some taper) but they have a special tip where you have a material cutting edge:

Click the image to open in full size.

Wikipedia distinguishes between them as:
Quote:
Thread-forming vs. thread-cutting
Self-tapping screws can be divided into two classes;[3] those that displace material (especially plastic and thin metal sheets) without removing it are termed thread-forming self-tapping screws; self-tappers with sharp cutting surfaces that remove the material as they are inserted are termed thread-cutting.
First ones are cheaper and ubiquitous, material cutting ones are more specialized and somewhat harder to find.

Name alone can be confusing since lots of people call all the same, which they are not.

If you want to buy some, browse catalogs carefully and specify the right code.
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Old 13th September 2020, 11:40 AM   #8
K-amps is offline K-amps  United States
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Thanks JMF, So I should be searching for Thread cutting screws...
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Old 13th September 2020, 05:57 PM   #9
K-amps is offline K-amps  United States
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Anything I find that is self threading, is #6-#8 or larger. I probably need something in the #3 or #4 width that will go through TO-220 cases.... Must be a specialty screw.
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Old 13th September 2020, 06:57 PM   #10
russc is online now russc  England
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Search for 'Cross Cut Tail Tapping Screws'.
Phew, that took some finding!
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