The Most Important Technical Data for All Do-It-Yourself Situations
Between screws, pipes, and dowels, countless cryptic technical data are lurking for the DIY enthusiasts.
Does an M8 hexagon screw mean that you can work with an 8mm open-end wrench? Does a ¾ inch water pipe now have an outer diameter of 19.05mm? These two questions show that so much in the DIY sector is highly technical. And because DIY enthusiasts are usually not professionals and often cannot look back on years of experience, there is always a risk for mispurchases, damage, and frustration, which can spoil the original desire.
Here, we will explain the most critical technical primary data for typical do-it-yourself situations and aids.
1. Hexagon head screws
They are the means of choice where a stable but detachable connection is desired. Whether you screw them with a nut or cut a thread into the (metal) workpiece: hexagon screws or also "threaded screws" can turn into a suitable internal thread, approximately a nut.
The length dimension of the screws always refers to the length between the tip and the point at which the head ends with the workpiece.
2. All other screws
In everyday life, DIY enthusiasts encounter numerous other screws that are dimensioned differently.
Length Dimension of the Screw
Up to top screw head
Up to the top of the cylinder
To underside round head
To widest point lens
To underside disc head
As a rule of thumb: with screws, the only thing measured is the part of the material that disappears.
3. Fresh water pipes
As far as pipes are concerned, there is - despite or because of standardization - dense fog here, which can immensely confuse the DIY enthusiasts. Also, the tubes that carry fresh water - both the tubes that lead to the tap and those that are involved in heating - are dimensioned differently from those that drain water.
In the case of fresh water pipes, it looks as if they used to be called in inches. Even nowadays, that the real dimensions are rounded millimeter values, is still leads to a somewhat complicated dimensioning.
Nominal Size (mm)
Dimension Round Tube (mm)
Dimension Copper Tube (mm)
12 x 1
16 x 2
15 x 1
20 x 2
18 x 1
26 x 3
22 x 1
32 x 3
28 x 1,5
4. Sewage and drain pipes
The sizes are different for everything that is installed from the washbasin and shower outlet, as well as downpipes from rain gutters. The big advantage is there is no inch-metric confusion in round millimeter values. The disadvantage in the nominal diameter is it does not refer to the inner diameter of the pipe, but to its outer diameter.
5. Torx screws
Torx profile screws have recently become the most popular screw on the market. No wonder, there is an enormously low risk of slipping out with the tool and the force can be transferred very well. But the problem is, the jaw widths are almost a "dimensionless number" because both in the inch and metric range there are enormously "crooked" values which refer to the outer diameter of the star and have nothing to do with the remaining dimensions of the screws:
Mouth Width (T-number)
D in Inches
D in Millimeters
But the whole thing has one advantage: On packs with Torx screws, the label always shows the T number as well as the dimensions of the screw, so you only have to grab the right bit. However, this makes it much more difficult to get a certain "sense of proportion" over time, unlike the hexagonal bolts.
We come to a point which, fortunately, is entirely logical and is dimensioned in half-millimeter increments, drill bit. Here, there are a lot of different measurements, but for the DIY enthusiasts, only one of them is interesting: the diameter. And the same applies here, no matter what type of drill you use: Nominal diameter is equal to the outer and inner diameter.
However, since you also have to clamp it a few millimeters deep into the drill, you will often find a working range among the specifications. The working height is the maximum borehole depth that can be achieved with a drill (even if in reality, you could go a little deeper by using a different clamping method).
For more reference, we have recently reviewed the best Cobalt drill bit set in 2018.
Dowels are the essential intermediate piece between screws on the one hand and drills on the other. It also reflects their dimensioning. But don't worry, the basic principle is first: The outside diameter of the dowel must always be the same as the inside diameter of the drill hole (and thus also the outer diameter of the drill bit). Only with soft materials (such as pumice stones) may the dowel diameter be approximately one millimeter above the borehole diameter.
However, during the length dimensioning, the dowel splits up.
The minimum drill hole depth must therefore always be higher than the anchor length so that there is room for the screw at the rear. Also, the screw must be longer than the dowel.