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Hollo Bolt: How does it work?

In hollow rectangular solid material (RHS) construction, the hollo bolt (TM) was developed to fasten materials such as steel I-beams to this hollow but strong material. Hollo bolt fasteners are used around the world in the construction of multi-story buildings, bridges, highway overpasses and various other applications where solid metal hollows are fastened together. Find out more about how the hollo bolt works below.

hollo bolt usage

Flow drilling

Flow drilling is the process of drilling a hole through hollow structural materials, such as rectangular steel pipes, without actually removing any of the metal. The hole is automatically sealed around its edge as it is formed. A tool called a threaded roll then draws a thread on the circumference of the hole, allowing it to accept a standard threaded bolt as a fastener.

The Hollo Bolt

The Hollo-Bolt assembly has 3 parts, the cone, the body and also the threaded bolt. It is pre-assembled and comes in a wide range of sizes for various clamping requirements. The Hollo Bolt is created of mild steel, with a zinc coating to stop corrosion. Custom made Hollo bolts can be manufactured from high quality stainless steel. The Hollo Bolt can also be manufactured with a socket or button head, or with a countersunk set screw. Hollo bolts are manufactured in a variety of strengths to provide greater structural integrity than other types of fasteners. Contact Lindapter for more info.

Hollo Bolt Sizes

Hollo bolts are produced in sizes from 4 1/2 cm (1 3/4 inches) to eight cm (3 1/4 inches) long.

Advantages of Hollo screws

Due to the consistency of Hollo Bolts, a typical size may be chosen and used throughout the development project, saving time and inventory costs. Hollo Bolt fasteners also minimize the amount of welds that must be accustomed join metal to metal, reducing costs and increasing worker safety.

Hollo bolt insertion

The Hollo Bolt inserts into drilled flow holes in both the structural material and the element to be fastened, up to the bolt collar. The hex head of the bolt protrudes past the collar. Hollo bolts can be inserted at any angle of the material from 30 to 90 degrees.

hollo-bolt lindapter

Tighten the Hollo bolt

The Hollo Bolt is tightened by placing an open end wrench around the collar to hold it steady and placing an appropriately sized torque wrench on the hex head to tighten it. An electric key is being developed that can perform both functions at the same time. By applying torque to the hex head, the flanges on the body of the Hollo Bolt open, anchoring the fastener deep into the solid structural hollow material.

Hollo bolt sealing

Various sealants have been developed for Hollo Bolt to reduce water penetration. Information on these is available from the manufacturer, Lindapter.

How many Hollo screws to use?

At least 4 Hollo bolts must be used to fasten a plate to a solid structural hole. Typically, 8 Hollo Bolts are used, in a 2 column format, depending on the width of the plate. Measure carefully when placing the Hollo bolts through the adjacent faces of the structural hollow solid in order that the bolts don't acquire contact with one another.

lindapter hollo-bolt

Procedure to remove a pre-installed Hollo-Bolt

Using a pneumatic tool to remove the Hollo-Bolts:

  1. Put pneumatic hand tool in reverse mode - counterclockwise rotation.
  2. Place an appropriately sized wrench (depending on the size of the necklace) on the flats of the necklace to hold it in place.
  3. Use the pneumatic tool to loosen the bolt.
  4. Continue in reverse mode until the cone inside of the RHS at the opposite end of the bolt is released to drop into the RHS.
  5. The bolt can now be removed as can the sleeve by prying off the collar with a pinch or pry.


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