What Size BoxBolt Do I Need? | Quick Sizing Guide from LNA Solutions
Not sure which BoxBolt size to choose? You’re not alone. Whether you’re working with hollow structural sections or need a fast, no-weld solution, picking the right BoxBolt matters. In this quick guide, we’ll break down everything you need to know, clamping ranges, bolt diameters, hole sizes, and more, so you can spec your connection with total confidence.
Table of Contents
- What is a BoxBolt?
- When Should You Use BoxBolt?
- How Are BoxBolts Sized?
- How Do I Choose the Right BoxBolt Size?
- Quick Reference BoxBolt Sizing Chart
- Tools & Tips for Easier BoxBolt Installation
- FAQ
What is a BoxBolt?
BoxBolts are blind fasteners used for steel-to-steel connections, especially with hollow structural sections (HSS). You only need access from one side, and you don’t have to weld or drill through both walls.
It’s fast, strong, and certified for structural jobs. Think of it like an anchor bolt, but for steel.
When Should You Use BoxBolt?
Use a BoxBolt when:
- You’re working with HSS or steel where access is limited to one side.
- You want a code-approved connection that doesn’t involve welding.
- You’re in a job site where hot work isn’t allowed or power tools are hard to use.
It’s ideal for curtain walling, solar brackets, HVAC supports, stadium railings, and just about any HSS connection you don’t want to fuss with.
Check out the boxbolt here.
How Are BoxBolts Sized?
BoxBolts are sized by:
- Bolt diameter (from 1/4″ to 3/4″)
- Clamping range (how much material it can grip)
- Length/Size Number (Size 1, 2, or 3)
- Finish: zinc, hot-dip galvanized, or stainless steel
Important: The “size” number (1, 2, 3) refers to the bolt length or clamping capacity, not strength. Strength comes from the diameter.
How Do I Choose the Right BoxBolt Size?
Here’s a simple 4-step method to figure it out:
1. Measure Your Clamping Range
- Add up the total thickness of the materials you’re joining.
- Pick a BoxBolt with a matching clamping range (min to max).
2. Match Your Load Requirements
- Use the tensile and shear ratings to make sure your bolt can handle the forces.
- Bigger diameters usually mean higher strength.
3. Choose Your Finish
- Zinc: Indoor or low-exposure jobs.
- Hot-Dip Galvanized: General outdoor use.
- Stainless Steel: Corrosive or food-safe environments.
4. Use the Correct Hole Size
- Pre-drill holes based on bolt diameter plus 1/16″.
- Make sure you meet edge distance and spacing per AISC 360.
Take a look at our sizing chart!
Quick Reference BoxBolt Sizing Chart
| Product Code | Bolt Dia | Description | Clamping Range | Hole Size | Tensile (lbs) | Shear (lbs) | Torque (ft lb) |
|---|---|---|---|---|---|---|---|
| BQ1G08 | 5/16″ | BoxBolt Size 1 | 3/16″ – 1″ | 9/16″ | 5,071 | 5,917 | 18 |
| BQ2G08 | 5/16″ | BoxBolt Size 2 | 11/16″ – 1-13/16″ | 9/16″ | 5,071 | 5,917 | 18 |
| BQ3G08 | 5/16″ | BoxBolt Size 3 | 1-3/16″ – 2-5/8″ | 9/16″ | 5,071 | 5,917 | 18 |
| BQ1G10 | 3/8″ | BoxBolt Size 1 | 3/16″ – 7/8″ | 3/4″ | 9,718 | 10,985 | 33 |
| BQ2G10 | 3/8″ | BoxBolt Size 2 | 11/16″ – 1-5/8″ | 3/4″ | 9,718 | 10,985 | 33 |
| BQ3G10 | 3/8″ | BoxBolt Size 3 | 1-3/8″ – 2-1/2″ | 3/4″ | 9,718 | 10,985 | 33 |
| BQ1G12 | 1/2″ | BoxBolt Size 1 | 3/16″ – 1″ | 13/16″ | 13,015 | 12,676 | 59 |
| BQ2G12 | 1/2″ | BoxBolt Size 2 | 3/4″ – 2″ | 13/16″ | 13,015 | 12,676 | 59 |
| BQ3G12 | 1/2″ | BoxBolt Size 3 | 1-9/16″ – 3-1/8″ | 13/16″ | 13,015 | 12,676 | 59 |
| BQ1G16 | 5/8″ | BoxBolt Size 1 | 3/16″ – 1-3/8″ | 1-1/16″ | 26,199 | 29,578 | 140 |
| BQ2G16 | 5/8″ | BoxBolt Size 2 | 1-3/8″ – 2-3/8″ | 1-1/16″ | 26,199 | 29,578 | 140 |
| BQ3G16 | 5/8″ | BoxBolt Size 3 | 2-3/16″ – 3-1/8″ | 1-1/16″ | 26,199 | 29,578 | 140 |
| BQ1G20 | 3/4″ | BoxBolt Size 1 | 5/8″ – 1-5/8″ | 1-5/16″ | 36,932 | 33,804 | 221 |
| BQ2G20 | 3/4″ | BoxBolt Size 2 | 1-3/16″ – 3-1/8″ | 1-5/16″ | 36,932 | 33,804 | 221 |
| BQ3G20 | 3/4″ | BoxBolt Size 3 | 2-9/16″ – 4″ | 1-5/16″ | 36,932 | 33,804 | 221 |
Tip: This chart includes hot-dip galvanized BoxBolts with available load data. Always verify fit, torque, and spacing with LNA’s technical team. Check out the full table here.
Note: These numbers include a 0.75 reduction factor. Still, always check with your engineer before finalizing.
Tools & Tips for Easier BoxBolt Installation
Use a BoxSok:
This specialty tool speeds things up. It holds the shoulder steady while you tighten the core bolt with a wrench. One tool instead of two. Less risk of busted knuckles.
Install in 3 Steps:
- Insert BoxBolt through aligned holes.
- Hold the shoulder steady with a wrench or BoxSok.
- Tighten to the recommended torque.
That’s it.
Also, make sure your holes are smooth. Remove burrs. And always follow torque specs from the catalog.
FAQ
How do I know if my BoxBolt is torqued enough?
Use a torque wrench and refer to the spec sheet. Going by feel? Not worth the risk.
Can I install BoxBolts overhead?
Yes, you can. And if you’ve ever welded above your head, you’ll appreciate not having to do it again. BoxBolts are made for those awkward angles and hard-to-reach places.
Do BoxBolts meet building codes?
They do. BoxBolts are ICC approved, DIBt certified, and carry Lloyd’s Register type approval. These aren’t gimmicks. They’re legit structural solutions trusted across North America and Europe.
What if my steel thickness doesn’t match a standard clamping range?
Go up a size. You never want a bolt that’s too short for the connection. Still unsure? Contact LNA’s engineering team. They’ll guide you through the best match.
If you’re not sure what size to spec, or just want someone to double-check your setup, don’t guess. Get in touch with the LNA team. They’ll help you get it right the first time.
Last reviewed: July 17, 2025
