Blind Bolts vs. BoxBolts® vs. Hollo-Bolts for Steel-to-Steel Connections

When hollow structural sections (HSS) are involved, steel-to-steel connections can be difficult and time-consuming. In these situations, one side of the connection cannot be seen or accessed, typically because one of the steel structural components is hollow inside.

Traditionally, connecting a steel component to a hollow structural section involves on-site drilling or welding, which usually proves cumbersome and needs to be more refined (by painting or otherwise) when completed. Luckily, you can avoid this aspect of any steel connection project thanks to a type of bolt known as “blind fixing.”

True to their name, blind fixings offer a blind structural bolt solution. They typically come in three varieties: BoxBolts®, Hollo-Bolts, and blind bolts. Each type provides a differently engineered solution to the problems that hollow structural sections introduce. Still, they all share a standard function: eliminating the messy, time-consuming, and money-spending trappings of traditional methods.


Hollo-Bolts and BoxBolts® are functionally very similar, as they approach the mechanics of blind structural steel connection nearly identically. They feature a central bolt that, when tightened, travels along the bolt’s cylindrical body. As it does this, a series of panels along the body are bent outward, expanding to create restraints with enough evenly distributed tension to keep the connection extremely secure.

In conjunction with the tightening action of the bolt on the opposite side, these panels affix the two steel components in place without needing to access the other side. Considering this action is usually concealed while happening within one of the steel components, it is referred to as a blind structural connection.

One compromise that needs to be made when using BoxBolts® and Hollo-Bolts is making sure enough space is allowed for their tightening mechanism to operate properly. This is because they’re already relatively large, and the expanding sheath they use only makes them wider when properly attached. They’re also tricky to remove, but all of this is in service to an attribute that makes these bolts superior in the eyes of many: their resilience and security.

In steel-to-steel connection projects, accounting for what’s known as “shear resistance” is incredibly important since wind, weight, and other factors induce this type of force onto bolted structures. The extreme level of reinforcement introduced by the unique design of BoxBolts® and Hollo-Bolts makes them incredibly shear-resistant and, therefore, much more durable than their counterpart, the blind bolt.


Blind bolts serve the same purpose but accomplish it through a different engineering solution. Blind bolts employ what can be considered a “gravity-operated toggle” mechanism, meaning housed within the bolt is a bar that flips out from both sides of the cylindrical body. This bar extends on either side and simply travels closer to the blind side of the steel as the bolt on the other side is tightened. The mechanism is much simpler than a BoxBolt®, meaning they are easier to remove and require a smaller space to operate correctly.

However, this mechanism is much less secure than BoxBolts® or Hollo-Bolts, meaning blind bolts have a significantly lesser shear strength. For most steel-to-steel connections, strength and resilience are usually the top priority, especially for more ambitious construction projects. In lieu of that strength, blind bolts do offer greater flexibility, considering they are smaller and easier to remove.


When it comes to connecting hollow structural sections, the advantages of blind fixing solutions are numerous, from their non-destructive installation that offers a more straightforward install method and a cleaner appearance to their flexibility as they offer easier solutions to making adjustments. However, when choosing what type of blind structural bolt solution is best for your project, it’s essential to know what you prioritize the most: flexibility or strength.

While blind bolts serve a nearly identical purpose to BoxBolts® and Hollo-Bolts, the ease of use and adaptability they provide comes with a detrimental and potentially dangerous lack of shear-resistance, something extremely important in especially large or ambitious steel-to-steel structural connection projects.

However, while they require more space to operate, and larger entrance holes to be affixed, BoxBolts® offer a more structurally-sound solution with a shear-resistance unparalleled by other bolt-based hollow structural steel connections.



Simple Installation

Their unique design means BoxBolts® can be easily installed using basic tools, substantially reducing labor costs and project timelines.

Durable Connection

The BoxBolt’s® widening body ensures a connection that is reinforced beyond the measure of a typical bolt while also accomplishing that connection through a self-contained mechanism, meaning the working components are hidden from view.


Suitable for both indoor and outdoor use, BoxBolts® are ideal for various applications, including bridges, buildings, and industrial installations, especially when aesthetics are a top priority.

Three Distinct Available Finishes

Depending on the conditions the BoxBolts® must withstand, LNA Solutions offers three different finishes; Zinc, Galvanized, and for seriously demanding applications, Stainless Steel.


When it comes to steel-to-steel connections, BoxBolts® offer unparalleled advantages over traditional methods like welding or drilling. Here’s why they’re a preferred choice for modern construction projects:

Time and Cost Saving

BoxBolts® eliminate the need for time-consuming welding processes, significantly reducing labor costs and project timelines. Not to mention, they require fewer tools and therefore less expertise to properly install.

Enhanced Safety

Welding can pose various safety hazards, such as exposure to fumes and risk of fire. With BoxBolts®, you can ensure a safer working environment for your team.

Flexibility and Adaptability

Unlike welding, which requires precise measurements and preparation, BoxBolts® offer greater flexibility, allowing for easier adjustments and modifications during installation.

Non-Destructive Installation

Welding can compromise the integrity of steel structures, leading to potential weaknesses and vulnerabilities. BoxBolts® provide a non-destructive solution, preserving the structural integrity of your steel components.


For some projects, a seamless, aesthetically pleasing look is paramount. To please architects and clients alike, BoxBolts® offer a very clean, uniform appearance once installed.

Tensile Strength

In welding, the quality of a weld determines its strength, and aside from just being unsightly, a bad quality weld means lesser tensile strength, which could be dangerous. When using BoxBolts®, you can be assured the tensile strength will be consistently high as long as weight is distributed evenly and the BoxBolts® are affixed properly.


The primary advantage of BoxBolts®, as well as other types of blind bolt solutions, is their unique status as “blind fixings,” meaning they can establish a secure connection between two steel components, which can be easily installed by one person when one side of the connection is difficult to access or unable to be seen. Normally, solving a problem like this would require welding, which has disadvantages such as its lack of consistent strength and a destructive connection that results in marring the appearance of the components welded together.

Not only do BoxBolts® possess greater strength than welded connections when applied properly, but they also reduce the likelihood of errors, generally reduce the cost of the work, and are easier to replace. This way, if a mistake needs to be amended or an adjustment has to be made shortly after installation, no cutting is involved in the removal process, as welded connections require. Instead, it’s as simple as unscrewing the connection, making the necessary adjustments, and reassembling.

Another method often used in these situations is “through bolting”. As the name suggests, through bolting involves using a double-sided bolt with a long enough body that spans from one side of the connection to the other. If this technique is used to connect a steel component to an HSS, the bolt needs to be long enough to come out the far side of the hollow component. Through bolting also requires the coordinated work of two people, something BoxBolts® eliminate the need for.

Compared to these other more conventional methods, BoxBolts® allow for a seamless, damageless, and aesthetically pleasing solution to a wide range of otherwise awkward or inaccessible steel-to-steel connection applications. BoxBolts® even include a corrosive-resistant finish, meaning the appearance, durability, and strength of BoxBolts® is built to last, and not susceptible to breaking down due to factors of nature.


Refer to LNA Solutions’ product page for more information on BoxBolts®, their applications, functionality, and available finishes. Contact us today to learn more about BoxBolts® and how they can revolutionize the appearance, safety, and timeline of your construction projects.



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