Which hole should I drill for the anchor bolt?

Material hardness

Brinell hardness is a characteristic that allows you to determine the hardness of a material.

Stainless steel fasteners are also equipped with special markings on the top of the fastener.

Type of steel A2 or A4 and tensile strength - 50, 70, 80, examples: A2-70, A4-80. Fasteners that have a clearly defined thread are color-coded for A2 in green and for A4 in red. The value for the yield strength is not specified.

For example, a value of 70 is the most standard and demonstrates the maximum strength of stainless steel fasteners.

Maximum fluidity for stainless steel hardware, often only a reference value.

The fluidity in this case will be 250 N/mm2 for A2-70 and about 300 N/mm2 for A4-80.

The approximate increase will be no more than 40%. In other words, this type of steel perfectly changes shape before irreparable deformation occurs.

Old domestic measurement methods according to GOST did not allow paying due attention to the maximum permissible loads on bolts, so the produced hardware was significantly lower in quality compared to modern ones.

An example to calculate the load on a material as accurately as possible using strength classification:

M12 fastening with strength 8.8, size d2 = 10.7 mm and maximum section length 89.87 mm2. In this case, the maximum permissible degree of load will be: (8*8*10)*89.87;0) = 57520 Newton.

Load chart for carbon steel and stainless steel bolts.

ST-4.6		ST-8.8		A2-70		A4-80
THREAD	d2, mm	Area 62, tt2	Max. load, Newton	Working load, kg	Max. load, Newton	Working load, kg	Max. load, Newton	Working load, kg	Max. load, Newton	Working load, kg
M1	0,8	0,5	121	322	10	126	151
M2	1,7	2,27	544	20	1 452	70	567	20	681	30
M3	2,6	5,31	1 274	60	3 396	160	1 327	60	1 592	70
M4	3,5	9,62	2 308	110	6 154	300	2 404	120	2 885	140
M5	4,4	15,2	3 647	180	9 726	480	3 799	180	4 559	220
M6	5,3	22,05	5 292	260	14 112	700	5 513	270	6 615	330
M8	7,1	39,57	9 497	470	25 326	1 260	9 893	490	11 872	590
M10	8,9	62,18	14 923	740	39 795	1 980	15 545	770	18 654	930
M12	10,7	89,87	21 570	1 070	57 520	2 870	22 469	1 120	26 962	1 340
M14	12,6	124,63	29 910	1 490	79 761	3 980	31 157	1 550	37 388	1 860
M16	14,6	167,33	40159	2 000	107 092	5 350	41 833	2 090	50199	2 500
M20	18,3	262,89	63 093	3 150	168 249	8 410	65 722	3 280	78 867	3 940
M24	21,9	376,49	90 359	4 510	240 956	12 040	94 123	4 700	112 948	5 640
M27	24,9	486,71	116 810	5 840	311 493	15 570	121 677	6 080	146 012	7 300
M30	27,6	597,98	143 516	7170	382 708	19130	149 495	7 470	179 394	8 960

We present to your attention an updated table of maximum loads on stainless materials and high-strength connections.

To be additionally confident in the safety of the load, you can, without a twinge of conscience, divide the load in Newtons by thirty.

Stainless steel A2-50
THREAD	d2, mm	Area d2, mm2	Yield strength, MPa	Max. load, Newton	Working load, kg
M1	0,8	0,50	200	100
M2	1.7	2,27	200	454	20
M3	2,6	5,31	200	1 061	50
M4	3,5	9,62	200	1 923	90
M5	4,4	15,20	200	3 040	150
MB	5,3	22,05	200	4 410	220
M8	7,1	39,57	200	7 914	390
M10	8,9	62,18	200	12 436	620
M12	10,7	89,87	200	17 975	890
M14	12,6	124,63	200	24 925	1 240
M16	14,6	167,33	200	33 466	1 670
M20	18,3	262,89	200	52 578	2 620
M24	21,9	376,49	200	75 299	3 760
M27	24,9	486,71	200	97 342	4 860
MLO	27,6	597,98	200	119 596	5 970

Stainless steel A2-70
THREAD	62.mm	Area d2, mm2	Yield strength, MPa	Max. load, Newton	Working load, kg
M1	0,8	0,50	250	126
M2	1,7	2,27	250	567	20
M3	2,6	5,31	250	1 327	60
M4	3,5	9,62	250	2 404	120
M5	4,4	15,20	250	3 799	180
MB	5,3	22,05	250	5 513	270
M8	7,1	39,57	250	9 893	490
M10	8,9	62,18	250	15 545	770
M12	10,7	89,87	250	22 469	1 120
M14	12,6	124,63	250	31 157	1 550
M16	14,6	167,33	250	41 833	2 090
M20	18,3	262,89	250	65 722	3 280
M24	21,9	376,49	250	94 123	4 700
M27	24,9	486,71	250	121 677	6 080
MLO	27,6	597,98	250	149 495	7 470

Stainless steel A4-80
THREAD	12, mm	Area d2, mm2	Yield strength, MPa	Max. load, Newton	Working load, kg
M 1	0,8	0,50	300	151
M2	1,7	2,27	300	681	30
M3	2,6	5,31	300	1 592	70
M 4	3,5	9,62	300	2 885	140
M 5	4,4	15,20	300	4 559	220
MB	5,3	22,05	300	6 615	330
M 8	7,1	39,57	300	11 872	590
M10	8,9	62,18	300	18 654	930
M12	10,7	89,87	300	26 962	1 340
M14	12,6	124,63	300	37 388	1 860
M16	14,6	167,33	300	50199	2 500
M20	18,3	262,89	300	78 867	3 940
M24	21,9	376,49	300	112 948	5 640
M27	24,9	486,71	300	146 012	7 300
MLO	27,6	597,98	300	179 394	8 960

Fastening to structures made of weak materials

The definition of “weak” materials includes plasterboard, porous (light) concrete, and hollow brick.

The general rule for drilling holes in the listed materials is to exclude the impact mode.

It is recommended to use nylon dowels. Their diameters should be larger than for structures made of solid concrete or brick. The diameter of the hole is 2 mm smaller than the dowel hole.

Butterfly dowels are suitable for fastening to walls made of sheet material (plasterboard, chipboard, OSB, etc.).

Types of dowels

Dowel type Driva

Perhaps the most popular fastener for plasterboard sheets. It comes with or without a drill, metal or plastic. When making a hole for its fastening, use a drill with a diameter of 8 mm. The manufacturer declares the working shear load that gypsum board can withstand using this dowel is 25 kg, while the maximum load is up to 50 kg.

The popularity of the Driva dowel is due to its fairly high reliability and relatively low price. The strength of such fastening is achieved by distributing the load over a large area, which is ensured by the shape of the dowel.

Driva drywall dowel is simple and effective

Flat dowel nail

This dowel is made of fire-resistant steel, is quite simple and easy to use, since it does not require additional drilling and, accordingly, eliminates dust. It can be hammered into the drywall with a hammer or pressed in by hand if you can do it.

The principle of operation of a dowel-nail is that when a self-tapping screw is screwed into it, the initially flat front part opens up, forming a reliable stop.

It is used for sheets up to 12.5 mm thick inclusive. Self-tapping screws are chosen with a diameter of 3.5-5mm. The working load for pulling out, declared by the manufacturer, is 15 kg, for shearing - 30 kg, the maximum shear load, obtained experimentally, is 48 kg. Among other things, the dowel-nail is reusable, that is, it can be dismantled and mounted in another place several times.

The flat dowel-nail for drywall is very convenient to install, as it does not require drilling

Universal expansion dowel Butterfly

The butterfly dowel is suitable for both drywall and concrete bases. The hole for its installation is drilled with a drill with a diameter of 8 mm, the diameter of the complete self-tapping screw is 4.5 mm.

For the butterfly dowel, we recommend using self-tapping screws without missing threads, since when screwing in, having reached the smooth neck, the self-tapping screw will begin to scroll, and the dowel will not take the desired shape as a stop.

In general, the plastic butterfly dowel works approximately the same as the others, creating a stop behind the gypsum board when screwing in the self-tapping screw. The shape of this stop is somewhat reminiscent of a butterfly, hence the name of the fastening element. The calculated working load on the dowel is 25 kg, the maximum load is 55 kg.

The Butterfly dowel for drywall is the most popular because it is equally inexpensive, convenient and effective.

Dowel Molly

The Molly dowel, or rather the Molly anchor (after all, it is an independent fastening unit that does not require an additional screw) is another popular type of fastening for drywall, made of metal. This dowel, unlike the previous ones, is available in various sizes and, accordingly, for various loads.

For example, for Molly of the minimum size marked 4/16/38 (4 is the diameter of the screw, 16 is the length of the neck and the maximum thickness of the sheet for which it can be used, 38 is the total length of the element), the working load is 25 kg, the limit for cutting is 47kg.

To make holes for Molly, choose a drill 2 times larger than the diameter of the neck (the first number in the marking), that is, for a four it will be 8 mm, for a six it will be 12, etc.

To install the Molly dowel, you need a special tool that brings the fastening element into “combat readiness”. With its help, the screw is slightly pulled towards itself, while the hooks bend. Then you can turn the screw with a screwdriver, bending the hooks until they stop. All this should be done by inserting a dowel into a hole in the drywall.

If there is no special tool, you can activate the anchor using wire cutters (side cutters) or even a regular flat-head screwdriver.

Molly dowel for drywall - a solution for professionals

Fischer plastic twist dowel

When a self-tapping screw is screwed into such a dowel, the latter twists, forming a stop behind a sheet of drywall, hence the name of the fastening element. The drilling diameter for such a dowel is 8 mm, the screw diameter is 5 mm.

When tightening a self-tapping screw, the main task is not to pinch too hard, otherwise it will begin to rotate and the fastener will need to be re-done. For this reason, when using a screwdriver for tightening, set it to the minimum speed.

The working load for tearing off a twisting dowel is 10 kg, for shearing - 25 kg, crash load - 70 kg.

Twistable plastic dowel for drywall - an interesting and effective solution, backed by Fisher reliability

What to consider when choosing a drill for a dowel

Selecting a drill to create a hole in which the dowel will be fixed should take into account:

the material from which the wall itself is made, as well as its finishing;
expected loads of the fastener.

You should also choose a drill depending on the diameter of the fasteners used. On the outer surface of factory-produced dowels, as a rule, there are markings that allow you to correctly select drills of the appropriate diameter for them.

Table 1. Selection of drill and screw for dowel

It is important to know not only how to choose a drill for a dowel, but also how to drill a hole correctly. If it is necessary to drill a hole in the wall for a dowel, the diameter of which is 10 mm, then first use a drill with a diameter of 8 mm and an impact drilling mode. After the hole is drilled, the tool is replaced with a drill with a diameter of 10 mm and is used without using the impact drilling mode. This approach will allow you to get a hole in the wall of the required diameter with smooth and neat edges.

If you need to drill a concrete wall, it is better to use a Pobedit drill, which can handle such a durable material without any problems. The selected cutting tool must be at least 3 mm longer than the dowel itself. If you neglect this requirement, the dowel will not completely fit into the resulting hole, in the final part of which dust and pieces of crumbled material, as a rule, accumulate. In addition, the shape of the bottom of the hole may not match the shape of the tip of the fastener.

Calculate the drilling depth with a margin relative to the dowel length

Criterias of choice

The dowel dimensions are selected based on the following factors.

Supporting material

. Dowels of the same length and diameter, made of the same material, can withstand greater loads in concrete structures than in brick ones. But this fastener is not suitable for fastening massive objects to foam concrete - it does not hold significant weight and comes out of the installation hole. In such cases, chemical anchors should be used.

Load per fastener

. The greater the design load, the more attachment points required. Before purchasing, pay attention to the maximum permissible and recommended load indicated on the packaging.

Location

. The prevailing load depends on it: along (axial, tearing) or across (for fracture and bending) the axis. In the first case, the length of the fastener matters, in the second – the diameter.

Allowable hole depth

. A large load requires a maximum dowel size.

How deep will the screw be screwed in?

. This is true for fasteners located horizontally: the closer the screw head is to the wall surface, the lower the fracture/bending load and the shorter the permissible length of the fasteners.

For light items

Light objects are attached to structures made of brick and concrete with plastic dowels with a diameter of 6 mm and a screw. The drill is selected to be of equal diameter. The length of the dowel for fastening to the wall and ceiling is 4 and 6 cm, respectively (the values given are minimum). The depth of the mounting hole is 5 mm larger.

For medium weight items

A dowel-nail, which is a fastening pair, copes with the task. One of the advantages of its use is the speed of installation (the name is “quick installation dowel”). The mounting sequence is as follows:

a hole of the selected diameter and depth is drilled;
dust is removed from the hole;
a plastic part of the fastening pair is installed;
The “nail,” despite the presence of a thread, is driven in with a hammer, which gives a gain in time during installation (compared to a screw).

The diameter of the dowel used in this case is at least 8 mm. Length – 6 and 8 cm for mounting to the wall and ceiling. The diameter of the drill is selected similarly to the considered method “for light objects.” Number of fixation points – up to 4.

For heavy objects

Massive objects (TV stands, bookshelves, furniture cabinets, equipment) are fastened with hardware with dowels, the diameter of which is at least 10 mm. The lengths for fastening to walls and ceilings are 6 and 8 cm, respectively. The number of fixation points is at least six.

Fastening medium-weight products

Objects weighing between 5–10 kg are secured with impact dowels Ø8 mm, a drill Ø8 mm, but always with a Pobedit tip. The fastener should extend into the wall cavity by 6 cm, and if the ceiling is 8 cm. To secure an object weighing up to 10 kg, 4 fasteners should be used.

Read also: Comparative characteristics of steels u7 u8 u9

Methods for securing a dowel in a large hole

What should you do if the hole drilled in the wall is larger than the dowel? Professionals recommend following the following methods of fixing a dowel in a wall:

Using a repair cloth. It means a piece of special material that is wrapped around a dowel and then placed in a hole made in a brick, aerated concrete, or concrete wall. Before “wrapping”, the napkin must be moistened in water. Once the fastener is wrapped, it is driven into the gap. Next, you need to wait until it hardens - about two to three minutes. Then, you can insert a self-tapping screw, screw and other fastening devices.
Use a 2-component composition. It means a special type of glue, which contains polyurethane without styrene, which is safe for the human body. The package, which resembles a syringe, contains a 2-component composition.