Anyone who has learned a construction trade will be familiar with this saying: “And the foreman didn’t want to believe it – you can also screw with a hammer”. This enigmatic admonition to always use the correct tool has now been caught up by technical development: Because impact anchors and nail anchors are actually a fusion of screw and nail, which can be treated with both a hammer and a screwdriver. Read everything you need to know about knock-in anchors and nail anchors in this article.
Dowels – firm but laborious
Inserting a dowel in a wall requires various tools and is therefore quite time-consuming: First, a hole is drilled, then the plastic dowel is inserted and then the wood screw is screwed in. To do this, you either have to have two drills ready to hand or you have to constantly rebuild the existing machine: drill bit out – bit in and vice versa. This is very annoying and time-consuming in the long run. Especially in professional use, the call for a more efficient method became louder and louder. For this reason, the dowelled connection was developed, which can be driven in with a hammer and loosened again with a cordless screwdriver.
Function – impact anchor
How does a drive-in anchor work?
The drive-in dowel basically consists of the same components as a normal dowel connection: A nylon or PP dowel is inserted into a drilled hole. The inserted screw spreads the dowel so far apart that it clamps against the inner wall of the drill hole. The difference between the normal screw-dowel connection and the drive-in dowel is that the screw is inserted with a hammer blow. This is not only faster, it also saves you the hassle of converting the cordless screwdriver. In the workflow, the cordless screwdriver or drill can only be used to set the drill holes. Since every decent builder has a hammer hanging from his belt, it can be hammered in in a matter of seconds.
The terminology of “hammer-in anchor” and “nail anchor” is not entirely clear-cut. Both terms currently mean the same thing. The variants of this product are very diverse.
Special features of knock-in anchors
The normal knock-in dowel differs from the normal dowel connections in its geometry: normal knock-in dowels are longer and thinner than screw-in dowels. This is because:
In order for the screw to drive into the anchor, it must be straight and firmly in the wall. To do this, it is already inserted so far into the dowelled hole that it can no longer wobble. For this purpose, the long and thin geometry is ideal. Another reason is the friction and clamping force: it is the clamping connection between the dowel and the wall that creates the firm connection. The larger the surface area of the anchor, the more firmly it can sit in the wall. Large screw anchors can therefore cope with a relatively short drilling depth. However, in order to achieve the same strength, the dowel that can be driven in must be correspondingly longer. Nevertheless, knock-in anchors do not quite reach the load-bearing capacity of screw anchors
The ability to hammer in these dowels is additionally supported by the fact that the screw has a large, flat head and the dowel also has a wide ring on its shank. The ring acts as a buffer that can cushion the impact of the driven-in screw.
What is particularly ingenious about knock-in anchors and nail anchors is that the screw can be unscrewed normally with a screwdriver. However, only a motor-driven screwdriver should be used, otherwise you can easily get tendonitis in manual operation.
The leading manufacturers of drive-in anchors are the companies FISCHER and WÜRTH. At this point we would like to introduce you to the most common types of nail plugs from these suppliers.
FISCHER nail plugs
Nailable plug NS
The nail anchor NS is a unit made of nylon anchor and galvanized nail screw made of high-strength, stainless steel. In order to make the installation as efficient as possible, these knock-in dowels are already pre-assembled into one unit. This is very advantageous, especially in series assembly. The NS has an integrated impact lock. This prevents the plastic anchor from spreading prematurely. The nail head has a cross-slot mount and can be easily unscrewed with a cordless screwdriver. When screwing in again, the screwdriver is also recommended.
The NS is available with a drill core diameter of 5 to 10 millimeters and a length of 30 to 230 millimeters. Its prices start from 0.06 euros per piece. However, these low prices are not available in unit prices, but only in bundles of at least 50 pieces. The manufacturer Fischer offers a total of 26 different types of NS dowels.
The instructions describe the NS as suitable for through-hole mounting.
Nailable plug NF
The nail anchor NF has an enlarged slot on the shank of the nylon anchor. As a result, it can spread out more than the NS. Technically, however, both dowels are quite similar. The NF also has an impact lock. It is well suited for substructures made of metal or wood. This also includes profiles for the wall connection or auxiliary rails for plastering. It is conditionally suitable for cable platforms: Here, the load capacity should be calculated precisely and adhered to. To be on the safe side, a stronger anchor should be used for undetermined shear forces. However, the NF knock-in anchor can be used to fix foils, perforated straps or clamps. All normal materials for solid masonry and their high-hole variants can serve as load-bearing building materials.
The NF is available with a drill core diameter of 5 to 8 millimeters and a length of 25 to 120 millimeters. Its prices start from 0.10 euros per piece. However, these low prices are not available in unit prices, but only in bundles of at least 50 pieces. The manufacturer Fischer offers a total of 19 different types of NF dowels.
The instructions also describe the NF as suitable for through-hole mounting.
Nailable anchor NP
The characteristic feature of the NP knock-in anchor is its wide mushroom head. This makes it particularly suitable for fastening components with low material thickness in the visible area. The wide mushroom head and the correspondingly wide head of the impact screw ensure a particularly strong connection of thin material. Even with vibrations on the structure, tearing in the material is prevented by the large contact surface. This makes the nail anchor NP ideal for sheet metal, foils and signs, even if they are in the field of vision.
Its installation guide describes it as suitable for through-hole mounting.
The NP is available with a drill core diameter of 5 to 8 millimeters and a length of 30 to 40 millimeters. Its prices start from 0.06 euros per piece. A single purchase is possible. The manufacturer Fischer offers a total of 6 different types of NP dowels.
Nailable anchor NP K
The nail anchor NP K differs from the NP in one very important detail: the hammer-in anchor NP K is made entirely of plastic. This reduces its carrying capacity considerably. However, this nail anchor has not been developed for carrying heavy loads. Its task is to make an electrical installation as safe as possible. The absolutely non-conductive knock-in anchor is ideal for setting electrical installations. Above all, cable ducts made of thin-walled sheet metal or plastic can be ideally fastened with this knock-in anchor. With its mushroom head, it has the same advantages as the NP nail plug.
Its installation guide describes it as suitable for through-hole mounting.
The very limited task of the NP K makes a large selection of variants unnecessary. This is why the plastic knock-in anchor is only available in one version. The prices are around 0.07 euros per piece.
Nailable anchor NS D
In contrast to the NP K, the nail anchor NS D is a real hard worker. Basically, the NS D is a simple NF. Thanks to an integrated sealing washer and an impact screw made of high-strength, galvanized and stainless steel, this impact anchor is particularly suitable for outdoor use. Not only is it corrosion-resistant itself. The large sealing disc ensures a wide contact pressure and a seal from the outside to the inside. This makes the NS D particularly suitable for areas that are exposed to the weather and impact water. The wide contact surface is ideal for processing thin-walled materials such as sheet metal and signs. Foils can also be attached well with it.
The nail anchor NS D is only available in two variants. They differ mainly in the diameter of the sealing washer and in length. You need a drill hole diameter of 6 millimeters and are 40 and 60 millimeters long. Prices start at
WÜRTH nail plugs
The main difference between WÜRTH nail plugs and FISCHER products is that they are mostly made of metal. Of course, that makes them much more expensive. However, they are also primarily intended for special applications where large shearing forces can occur.
Hammer-in anchor WS-D/ external thread WS-D/ internal thread WS-D
This metal drop-in anchor is designed for ceiling mounting of light to medium loads. It is mainly used to fasten thermal insulation. The instructions stipulate that it is used for non-structural multiple fastenings. The instructions also require the use of collar drills. Würth offers the WS-S in five sizes. The dowel length is 38 – 114 millimeters. Würth only sells to traders, so no information on prices can be determined.
The knock-in anchors with internal or external thread are very practical for the simple installation of bulky trailer loads. According to the instructions, these dowels are only designed for light loads. Flange drill bits are required for the drill hole. They can only be inserted in solid concrete. The load-bearing capacity of the WS-D anchor is generated by frictional force. The prices for the threaded versions of the WS-D are only visible to registered webbing users.
The nailed anchor W-SD WSS 2/L expands the WS-D anchor with an integrated fastening module for suspended ceilings and thermal insulation. With this system plug, a decoupling from structure-borne noise is created. This makes its use for apartment buildings very interesting. The instructions also require the use of collar drills for this dowel in order to be able to drill the hole as smooth as possible. The loads are only held by frictional force. The fully galvanized plug is particularly resistant to rust. The prices are only visible for registered customers also for this special plug.
Drive-in anchor W-SD WSS 3/L
In addition to the dowel-screw unit, this special dowel has an integrated mounting rail. It is primarily used for the direct installation of ventilation ducts
Drive-in anchor W-SD WSS 1/L
The special dowel W SD WSS 1/L has an integrated bracket for installing sound-insulating suspension systems and mounting rails. It is equipped with an integrated rubber buffer, which largely decouples it from structure-borne noise.
Buy knock-in anchors and nail anchors
As with all small building products, the prices depend heavily on the quantity purchased. It is important that you do not just buy straight away or only look for the cheapest prices. Drive-in dowels must always be laid strictly according to the instructions. The instructions indicate how deep the borehole has to be. The instructions also prescribe the drill to be used. Great attention and care should be paid to this so that the assembly does not fail due to the wrong execution.
Tips for speed readers
- Use drive-in dowels for large series
- Always use the right dowels
- Compare prices and purchase as large quantities as possible
- Always install exactly according to the instructions