Build a bolt: The open STEM building system for 3+

After 3D printing a few toy cars for my 3-year-old, I quickly discovered a harsh truth: durability is no match for toddler enthusiasm. Within a week, most of them were in pieces, wheels lost, axles snapped, and tiny tears of frustration shed (mostly mine). But instead of giving up or printing the same things over and over, we decided to flip the script.

Why not create something that he could build, break, and repair himself?

That idea turned into something bigger: a modular, repairable, build-it-yourself system, designed with kids in mind, but flexible enough for anyone to start creating, printing, and sharing their own parts. Think, Duplo meets open-source engineering.

Examples:
Digger (Link)

A Simple, Durable, Rebuildable Standard

We wanted to design a system based on repeatable, printable components, using dimensions and structures that were easy to understand and modify. Here’s the foundation:

Bolts (Link)

• Thread type: ISO Metric profile.
• Dimensions: M15x1.5, with the height doubled (for extra stability, usability and easy overhang printing).
• These sturdy connectors form the backbone of the system, easy to print, strong enough to survive real-world play.

Nuts (Link)

• Derived directly from the bolt thread.
• Scaled 1.05x in width to ensure a snug but not-too-tight fit, no matter the material or nozzle size.
• Subtracted from a solid to form a clean, printable internal thread in the nut.

Brackets (Link)

• Built around a 16mm central hole.
• Reinforced with a 2mm wall, spaced with 3mm, then reinforced again with another 2mm layer.
• Final bracket width: 20mm.
• These let you mount, rotate, or connect parts, perfect for mechanical toys, robots, or wild contraptions.

Wheels (Link)

• Modeled around an existing bearing design.
• Added tracks for extra grip when racing over the rug.

Why an Open Standard?

Because creativity shouldn’t be locked in a box. Our goal is to create a free and open system that anyone can expand. If a part breaks, print a new one. If a kid has an idea for a spaceship wing, design it and bolt it on. If someone wants to remix your design to make it even cooler, let them.

This isn’t just about toys. It’s about teaching problem-solving, design thinking, and hands-on engineering, skills that go way beyond playtime.

How You Can Get Started

1. Download or print the core parts: bolts, nuts, brackets and wheels.
2. Design your own creations around these common dimensions.
3. Modify and remix: try new shapes, experiment with materials, add hinges, gears, wheels.
4. Share your designs with others so the system grows as a collaborative toolbox.
5. Let kids do the building: watch them invent worlds from their imagination.
    

The Future Is Modular

We’re inviting makers, parents, educators, and kids to be part of something open, adaptable, and fun. Whether you’re printing at home or teaching in a classroom, this standard is meant to grow with you.

Break it. Rebuild it. Make it better and share it!

Want help building your first part or modifying your own? Let me know—I’m happy to provide templates, CAD files, or even design suggestions.