Contents
- How is a self-tapping screw different from a screw
- Types of self-tapping screws
- Choice of screw length
- Diameters and lengths of self-tapping screws with countersunk head GOST 1145-80 and semi-counter head GOST 1146-80
- Lengths and diameters of self-tapping screws with a semicircular head according to GOST 1144-80
- How to choose wood screws
- The choice of self-tapping screws for metal
- Length and diameter of roofing screws of different types
Screws, screws, bolts – these types of fasteners have been used for a long time, but there are also self-tapping screws. What is it and what are their features? What are the types of screws, how to choose them?
How is a self-tapping screw different from a screw
Let’s start with definitions. A screw is a fastener with an external thread applied to the rod. When joining parts, the male thread of the screw aligns with the female thread on the hole in the part or parts. So for the installation of the screw, you must pre-drill a hole. A screw differs from a screw in that it has a smooth tapering at the end and more rare threads.
And now attention. Self-tapping screw is short for self-tapping screw. It differs in that it does not require a pre-drilled hole for installation. When screwing in, he himself cuts the required grooves. Hence the term self-tapping. And so that the self-tapping screw can “bite” into the material itself, its thread is triangular, with sharp edges and, as a rule, more “deep”. So, a self-tapping screw is a type of screw that itself drills a hole in the material as it is twisted.
If we talk about the difference between self-tapping screws and screws, then the self-tapping screw has a more elongated and sharp edge. With this form, it is easier to “bite” into the material. To install self-tapping screws, a screwdriver is usually used, which allows you to do a large amount of work, unlike using a conventional screwdriver. It is not easy to overcome the resistance of the material when cutting a hole.
Types of self-tapping screws
Self-tapping screws are divided according to the field of application. They are universal, for wood, metal. These are the three main and large groups. There are even more highly specialized ones – for concrete, drywall (gypsum plasterboard) and gypsum fiber sheets (GVL). There are separate groups for window profiles and roofing materials.
However, keep in mind that if they talk about self-tapping screws for metal, they mean sheet metal or profiles from it. And then, in sheets of large thickness, holes are often pre-drilled. It is easier and faster to install fasteners, especially if they do not shine with quality.
Moreover, holes are often drilled in wood for self-tapping screws. In dense wood – such as oak – this is almost an immutable rule. The density of such wood is high and otherwise the process is too slow. In soft wood, holes for the installation of self-tapping screws are drilled for a different reason – so that the tree does not crack. When the screws are placed almost on the edge, this is possible. Here they are insured. In any case, the diameter of the hole for installing the self-tapping screw should be 1-2 mm smaller than the diameter of the fastener. Only under this condition will it be easy to install, and the strength of the connection will be normal.
There are also universal screws. But this does not mean that they are “for everything”. This means that they are optimal when you need to combine wood and metal. And for connecting metal-metal, wood-wood – it is better to take your own narrow-profile fasteners.
For wood and metal – the difference
What is the difference between self-tapping screws for wood and metal? First of all – different thread pitch. For installation in a tree, the carving is more rare. This is quite enough to gain a foothold in the fibrous structure. The self-tapping screw for metal has denser threads. Another difference is in the metal used for the manufacture of fasteners.
Even self-tapping screws for metal can have not just a narrowing with thread, but additional planes – a drill. Such fasteners can drill holes in sheet metal up to 5 mm thick. So that the edge of the self-tapping screw does not slide over the surface of the metal (and wood, too), the installation point is “punched”. With the help of a punch and a hammer, a small dent is left. It is not necessary to punch through the metal. It is enough that the screw of the self-tapping screw falls into the recess.
Metal and processing method
Self-tapping screws are made of carbon steel, stainless and brass. In the vast majority of cases, we use self-tapping screws made of carbon steel. They are not as expensive as stainless steel, but quite durable if you choose the right one. However, steel self-tapping screws can be of different colors: white, yellow and black. They are dyed after processing. Blacks are obtained by oxidizing and phosphating, yellows are obtained by anodizing, and whites are usually galvanized. There are also yellow galvanized ones.
What color self-tapping screws is better to choose? Looking for what material.
If for wood, the best choice is anodized. These are yellow. Yes, they are much more expensive than black ones. But black oxidized rust and then leave streaks on the wood. For metal, this is not critical, since usually the joints are painted over so that they do not rust. But there is another point: black oxidized self-tapping screws can be brittle. If you “twist” it during installation, the head may fly off.
Not only can this happen during installation, it also happens under load. For example, when the flooring was screwed to the logs with black oxidized self-tapping screws. Boards are known to bend and dry out. And this leads to increased loads on the fasteners. And the hats of black screws often fly off. This can be seen when the bulkhead floor. Flying off hats, by the way, may be the reason that some boards begin to arch or sway and creak more strongly. The fastener does not hold.
To install metal sheet material, it makes sense to take galvanized self-tapping screws. There will be no conflict of coatings and chemical reactions. In this case, they usually take white. Yellow is used for aesthetic reasons – when installing door hinges, locks, handles and other similar yellow accessories.
Types of self-tapping screws: head and slot
More self-tapping screws are divided by type of head. There are many types, but it is worth remembering that there are secret, semi-hidden and protruding (hemispherical, semi-cylindrical, etc.). Also available with hex heads. They are used to install roofing material, polycarbonate, fastening materials to fences, sheathing frames. In general, where rigid fixation is important. It is the screws with hexagonal heads that are usually equipped with sealing washers with rubber gaskets.
Self-tapping screws with countersunk heads are hidden in the wood during installation. In this case, it is not necessary to pre-drill holes of a larger diameter for the cap. To make the hat “like clockwork”, take hidden heads with notches.
The caps have a recess for the tool – this is the slot. This parameter is selected based on the available tool or bit. You can, of course, buy them – beats – but you should think about it in advance. And then buy fasteners and bits. If we talk about which slot is better, then at the moment it is considered the best Torx (torx), as it transmits torque best. This is important when working with hard material.
Choice of screw length
There are several rules for choosing the length of a self-tapping screw, which are used in different situations. When rallying / connecting two not very massive parts, the following selection rules work:
- So that you do not connect, the sharp end of the self-tapping screw should not stick out on the other side of the parts to be joined. That is, in any case, it must be shorter than the parts to be joined. Moreover, it is believed that the maximum strength will be if at least 5-6 mm remain to the edge of the lower part. Here also consider.
The length of the self-tapping screw is selected depending on the parts to be fastened. - On the other hand, the minimum self-tapping screw should enter the lower part by at least 1/3 of the thickness of the attached part. That is, if you fasten, say, a beam of 100 * 100 mm, then the minimum length of the self-tapping screw should be 1/3 longer. For this timber, the minimum length of the self-tapping screw is 100 + 100/3 = 133 mm. Take the next larger one. If you fasten a board 28 mm thick, then the minimum length of the self-tapping screw is 28 + 28/3 = 37 mm (usually 42 mm is chosen).
If some thin detail is attached to a massive base, another rule works. Then the length of the fastener should be 2-2,5 times longer than the attached part. So you need to select the length of the self-tapping screw, if you fasten something to the wall, say, or to the concrete floor. In this case, to fix the same 28 mm board to the wall, the fastener length is 56-70 mm. Here is such a difference.
Self-tapping screw sizes: the most applicable options
How to choose the length of the screws, it seems to be clear. Now about what they generally are. Here the situation is confusing. Neither screws nor self-tapping screws have a common standard. There are several standards for “worn out” years of manufacture, which specify the dimensions of some types of self-tapping screws.
- GOST 1145-80. Self-tapping countersunk head screws.
- GOST 1144-80. Screws with a semicircular head.
- GOST 1146-80. Screws with semi countersunk head.
The situation today is such that each manufacturer produces its own “line”. They are oriented, of course, to demand. Well, the parameters of the heads are usually made in accordance with one or another GOST. This somehow stabilizes the situation. Sometimes the assortment – diameters and lengths are also made according to the standard. In this case, in the description of the self-tapping screws, the diameters in which they are generally produced are indicated, and then there is a postscript: it corresponds to such and such GOST. This means that the heads correspond to the specified standard, and also that the assortment corresponds.
Diameters and lengths of self-tapping screws with countersunk head GOST 1145-80 and semi-counter head GOST 1146-80
| Diameter of the screw, mm | Self-tapping screw length, mm | Diameter of the screw, mm | Self-tapping screw length, mm |
|---|---|---|---|
| 1,6 | 7, 10, 13 | 4,0 | 13, 16, (18), 20, (22), 25, 30, 35, 40, 45, 50, 60 |
| 2,0 | 7, 10, 13, 16 | 5,0 | 13, 16, (18), 20, (22), 25, 30, 35, 40, 45, 50, 60, 70 |
| 2,5 | 7, 10, 13, 16, (18), 20, (22), 25, | 6,0 | (18), 20, (22), 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100 |
| 3,0 | 10, 13, 16, (18), 20, (22), 25, 30 | 8,0 | 50, 60, 70, 80, 90, 100 |
| 3,5 | 10, 13, 16, (18), 20, (22), 25, 30, 35, 40 | 10,0 | 80, 90, 100 |
How then choose self-tapping screws in length and diameter? Calculate / determine the length that is needed, determined with the type of head. Then they look at the diameters and make the final choice. Let’s say right away that for wood the principle “thicker means better” does not work. This can be applied to metal. For wood, thinner ones are better, but with good carvings and from good metal. Here is the ideal option.
But this is not enough. The store usually offers up to a dozen options of the same size, but from different manufacturers. And if it is more or less easy to decide on the metal and the type of processing, then it is difficult to choose which brand to take. There are, of course, proven ones, but they are expensive. Although, if you take cheap ones, 30-50% can go into marriage. What marriage? Then they bend, then the hats fly off. It’s not always, but often. If you are “lucky” to run into such fasteners, it turns out that buying “expensive” ones would not be more expensive. Well, not much more expensive.
Lengths and diameters of self-tapping screws with a semicircular head according to GOST 1144-80
| Diameter of the screw, mm | Bar lengths in mm | Diameter of the screw, mm | Bar lengths in mm |
|---|---|---|---|
| 1,6 | 7, 10, 13 | 4,0 | 13, 16, (18), 20, (22), 25, 30, 35, 40, 45, 50, 60 |
| 2,0 | 7, 10, 13, 16 | 5,0 | 13, 16, (18), 20, (22), 25, 30, 35, 40, 45, 50, 60, 70 |
| 2,5 | 7, 10, 13, 16, (18), 20, (22), 25 | 6,0 | (18), 20, (22), 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100 |
| 3,0 | 10, 13, 16, (18), 20, (22), 25, 30 | 8,0 | 50, 60, 70, 80, 90, 100 |
| 3,5 | 10, 13, 16, (18), 20, (22), 25, 30, 35, 40 | 10,0 | 80, 90, 100 |
Now compare the two tables. They are compiled according to different GOSTs. As you can see, the diameters and lengths match. This is what makes life easier. If in the manufacture of fasteners they adhered to the standard in terms of the ratio of diameter / length, then everything is simple. If not, then the manufacturer in the description of the screws attaches a table with dimensions (as in the figure above).
How to choose wood screws
It is not necessary to use self-tapping screws for metal or universal screws for fastening wood. Universal are good when you need to twist wood and metal. And when twisting two pieces of wood, they work worse. In the sense that specialized fasteners will hold the wood better. That is, we consider only wood screws. Believe me, there will be plenty to choose from.
As already mentioned, wood screws have a rarer thread with a higher profile (the grooves between the turns are deeper). They are used not only for wood, but also for all types of sheet materials: GVL, plywood, OSB (OSB), fiberboard and chipboard. Now about when which ones work best.
Carving and other “bells and whistles”
First you need to choose the type of hat. Secret or with a press washer, cylindrical, hemispherical – choose based on what kind of connection you need to make. It is also recommended to choose a TORX type spline, as it best transmits torque from a power tool. Next in order.
- It is necessary to decide whether the thread should be applied to the entire rod or not. If you need to fasten two pieces of wood and pull them tightly together, take a self-tapping screw with an incomplete thread. This means that under the hat there should be an area without threads. The length is equal to the thickness of the attached part or slightly more. Due to this zone, one part is “attracted” to another.
How to choose wood screws: a few chips for fast and high-quality work - To facilitate screwing into hard rock or sheet material, there are wood screws with a mill or mill. The cutter is only on self-tapping screws with incomplete threads. It looks like several screw-type notches that are applied before the start of the thread. Notches soften the wood, after which the self-tapping screw “goes” better.
- In general, wood screws have a thinner point and thus prevent cracking of the wood. But there are also special “gadgets” against cracking. It can be:
- grooves;
- cutting edges in the form of notches on the screw body;
- notches on several lower threads.
Are these bells and whistles necessary or is it a waste of money? As for the incomplete thread – this is not news. “Sits down” one detail on another is much denser. And try the rest. Only on your own experience will you understand whether it works or not, and what specifically suits you best.
And practical advice on choosing wood screws. It is important that the thread goes immediately from the very tip. If the first turn is too far or the tip is blunt, do not take it. There will be continuous torment, not work.
The choice of self-tapping screws for metal
Types of self-tapping screws for metal are more numerous, so understand and understand. They are definitely not made of brass – the metal is too soft. Self-tapping screws for metal are made of carbon and stainless steel. All types of heads are present, slots are also almost all available. There are two types of tips – with a sharp end and a drill. They are also divided according to the area of uXNUMXbuXNUMXbapplication – for indoors and for the street. They differ in the thickness of the protective layer. For the street, the coating should be thicker. Consider the most common types of metal screws.
Self-tapping screws with a press washer (seeds)
They differ in the head – it is wide and flat. A roller is formed along its edge, which presses the parts. This type of hardware is used not only for fastening sheet metal and products from it (for example, they assemble a frame for drywall). It can also be used if you need to fix plastic, plywood or fiberboard to wooden bars, metal or wooden frame. The flat and wide head presses materials well at the junction.
If you look closely at the head of the fastener in the photo on the right, you will see that the part has a rounded and almost flat shape. By the way, most of them are in stores and on the market. But this is not the best option for this fastener, although it is cheap. There are very few decent products of this kind. Often the slot is small, untreated metal that breaks or bends. But the most important thing is that even white galvanized self-tapping screws have a very thin layer of galvanization – 3 microns. It quickly collapses and the metal begins to rust.
If you look at more expensive metal screws with a press washer (pictured on the left), they have a trapezoidal head. It is higher, which allows you to make a deeper slot. They are also called “reinforced”. The quality of such fasteners is much higher. A deeper spline contributes to better torque transmission. This makes it possible, even without increasing the size of the self-tapping screw, to draw parts more tightly. For what? Due to the fact that the reinforced design can withstand more torque.
The sizes of self-tapping screws for metal with a press washer are not encouraging. Usually there is only a diameter of 4,2mm, and the length can be 13, 16, 19, 25, 32, 38, 41, 50, 57, 75mm. The package weight depends on the number of pieces. It can also be one of the criteria for assessing quality. In any case, the density of the metal and how accurately the dimensions are maintained. Because very often the rod is made not 4,2 mm, but 3,8-4,0 m, also in length. And the cap is thinner. In general, pay attention to the weight of the screws.
Self-tapping screws for GKL profiles
These are small black hardware. Sizes do not indulge in variety. There is one diameter – 3,5 mm and two possible lengths – 9,5 and 11 mm. For their small size they are called “bugs”. They are made of steel with zinc coating or phosphating. The head is a truncated cone, the slot is cross-shaped. A notch may be applied to the underside of the head. It serves for braking – it starts to cling to the relief on the self-tapping screw, which disables the rotation of the screwdriver.
The screw is pointed, there is a screw. Despite their small size, they drill metal up to 0,9 mm thick, and fasteners with a drill – up to 2,0 mm. But this is if they are of normal quality. Please note that this fixture is designed for indoor use. On the street, it quickly begins to rust, so do not use it outside.
Black self-tapping screws for fastening the plasterboard to the frame
The frame for drywall is assembled using “bugs” or self-tapping screws with press washers. The sheets themselves are attached to the frame using black self-tapping screws with a countersunk head and a sharp end. Made from phosphated steel, there are also galvanized. Actually, these are self-tapping screws for wood or metal. What to take to attach the GKL? Depends on what kind of frame you have. For wooden bars, take wood, for profiles – metal.
If you are plasterboarding a normal living space, black phosphated screws are a good choice. If the frame is assembled in the bathroom, kitchen, toilet, it is better to take galvanized ones. With high humidity, black ones quickly rust, then the heads fly off.
What are the dimensions of the drywall screws? The optimal diameters are 3.8, 4.0 and 4.2 mm. The length can be 16, 19, 25, 32, 35, 41. 45, 51, 55, 61, 65, 70, etc. up to 100 mm. What is the length of the self-tapping screw needed to attach the GKL sheet to the profile? Use the universal rule: double the length of the attached material. If you fasten drywall with a thickness of 12 mm, then the self-tapping screw is not shorter than 25 mm. Can it be longer? It is possible, but why?
Roofing screws
This is a type of fastener for outdoor use. This means that the protective layer is thicker. Roofing screws are easy to distinguish by their appearance. They have a hex head and a sealing washer. The washer can be rubber or silicone. Silicone is much more durable, but also more expensive. Good rubber, by the way, can also not crack for decades. It’s hard to tell if it’s good or not.
Roofing screws come in different types and they are designed to fasten different materials to frames of different rigidity. There are such types of roofing screws:
- Pointed. Designed for fastening soft material to a wooden crate.
- With short screw. This type is for fixing metal sheet material to wood.
- With long screw. This is for metal-to-metal fixation. It is most often used for fastening the profiled sheet to the frame of the fence.
Length and diameter of roofing screws of different types
| Type of roofing screw | Roofing screw diameter, mm | Roofing screw length, mm |
|---|---|---|
| Pointed | 4,8 and 5,5 | 25, 38, 50, 65, 80. |
| With short screw | 5,5 and 6,3 | 19, 25, 32, 38, 51, 64, 76, 102, 127mm For 6,3mm there are also 70, 80, 90, 102, 130, 150 and 170mm |
| With long screw | 5,5 and 6,3 | 25, 32, 38, 51 mm |
Roofing screws are made of galvanized steel. And it is better if galvanizing is galvanized. This coating is more durable. On top of the galvanized paint is sometimes still applied. Color – in tone with a coating. Washers are made either also galvanized or aluminum alloy. The washer was said to have a rubber or silicone seal. Rubber is better than EPDM, it does not lose elasticity for a long time even in the open air. The running dimensions of the roofing screws are given in the table.