What does "T5" refer to? 

Ron K. Jeffries

On Fri, Jul 10, 2015 at 12:01 PM, Werner Almesberger <werner@almesberger.net> wrote:
Designing that case is tedious work, but I'm beginning to feel that
I'm getting somewhere. But first, there's something important that
needs proper consideration: screws.

When looking for small screws, it's surprisingly difficult to find
detailed specifications. While Alibaba and friends are full of
offers of little Torx screws for iPhones (NB: Apple nowadays uses
pentalobe screws), Blackberry, etc., there's hardly a shop that
actually provides a specific geometry.

In general, it seems that Torx T5 is a good compromise between size
and availability. I.e., most of the screws used in mobile phones
seem to have a T5 drive.

So, what's the typical T5 screw like ? The answer is that there is
none. Drive (slotted, Phillips, Torx, ...), head shape (cylindrical,
conical, round, and all sorts of fancy variations), thread, and
length, while all being related to each other, can appear in many

Eventually, I found a combination that appears in several places:
Torx T5 drive with a M1.6 thread. The smallest head for this type
of screw seems to have a diameter of 3.0 mm and a height of
1.2 mm - small enough for Anelok.

This leaves the length. I found a lot of useful information in the
flyer for EJOT DELTA PT screws:

So for M1.6, we can have a length from 3.5 mm to 16.0 mm.

Next: the design so far.

- Werner

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