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I have a screw that is 1 1/2" long, and it has two different threads around it. It's a button head, made for a Phillips-head screwdriver.

What do you call this kind of screw and its threading so I can search to find more of this kind of screw?

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  • Hello, and welcome to Home Improvement. Interesting question; let's see if you get a good answer. – Daniel Griscom Apr 27 at 19:18
  • Is it double helical, or simply machined so that every other rotation is smaller? – Wayfaring Stranger Apr 27 at 20:26
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That type of threading is called hi-lo, or sometimes high-low.

From MutualScrew.com:

High-low screws -- or hi lo screws, as they are often called -- have double-lead threads (where two grooves have been cut around the shaft). This kind of screw includes a high thread and a low thread. The unique qualities of hi-lo thread specifications help minimize the amount of material displaced as the screw is driven into the material, while also serving to create a stronger grip than would otherwise be possible.

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