Learn how to choose magnet grades for DIY doors, jigs, tools, robots, and more by balancing size, pull force, heat, and real-world mounting limits. Read more.
The Rundown
Magnet grade links size, pull strength, and how the magnet handles heat.
Every build starts by choosing your main limit between space, force, or temperature.
Those numbers and letters help you match the magnet to real jobs like doors, mounts, and jigs.
Real holding power comes from the whole setup, not just the loose magnet on its own.
You’ve got a project idea in your head like a snap-shut enclosure, a removable sensor mount, a hidden latch, a tool holder that actually holds, or a modular jig that you can reconfigure without screws.
Then you start hunting for magnets, and the spec sheets hit you with a wall of letters and numbers like N35, N42, N52, N42SH, and the rest of them.
Here’s a more hands-on way to look at magnets. Magnet grade mostly tells you how much pull you can squeeze into a given size and how well that pull holds up when things run hot in use.
Once you understand that, the rest becomes a set of simple trade-offs you can knowledgeably choose instead of having to guess.
Step 1: Decide What Matters Most
The three constraints most DIY builds run into are size, force, or temperature. This is why you must decide what matters to you most.
You’re Space-Limited
If you can only fit a small magnet, a higher grade helps because you’re squeezing more performance into the same footprint. Grades like N42–N52 are common power-per-size options.
You’re Force-Limited
If your magnet needs to resist pulling, sliding, vibration, or shock (think drone payloads, mobile robots, car mounts, workshop fixtures, and so on), don’t assume that the strongest grade is the only answer. Force depends heavily on:
Air gap (even tiny gaps matter)
Contact area
Steel backing (if you’re using it)
How the magnet is loaded (pull vs. shear)
Grade helps, but geometry and mounting style often move the needle more than jumping from N42 to N52.
You’re Heat-Limited
Heat is where a lot of “it worked on the bench” builds fail. If your magnet site is near:
Motors
High-powered LEDs/heatsinks
Enclosure hotspots
Outdoor sun exposure (dark housings get surprisingly warm)
You’ll want to pay attention to the temperature letter codes (more on this next).
Step 2: Decode “N42” and the Temperature Letters
The numbers (N35/N42/N52)
That number is shorthand for the magnet’s maximum energy product (often shown as BHmax). In practice, a higher number = more strength potential at the same size. It’s not always that simple, but that’s a generally helpful way to look at it.
The letters (M, H, SH, UH, EH, TH)
These letters are about temperature tolerance, or how well the magnet resists permanent loss of strength as temperature rises. Typical ranges you’ll see listed are roughly:
No letters: up to ~80°C
M: ~100°C
H: ~120°C
SH: ~150°C
UH: ~180°C
EH: 200°C
TH: ~ 230°C
The quick takeaway:
If your project gets warm, “N42” isn’t the whole story. N42SH may outperform N52 in the real world if N52 is running too hot.
You can also use a manufacturer-grade reference table to sanity-check typical properties like temperature and coercivity trends.
Step 3: Match the Grade to Common Maker Scenarios
Snap-Fit Doors, Lids, and Hidden Latches
If your parts line up tightly (minimal gap), N35-N42 often feels great.
If you’ve got a painted surface, tape, or a bit of misalignment, move up in size first, then grade second.
Tool Holders and Wall Mounts
Your enemy here is usually shear, not straight pulling forces.
A smart move is using a steel plate/backer and designing a pocket so the tool load transfers into the body, not the magnet.
Robotics and Vibration-Heavy Builds
Prioritize mechanical capture (pockets, lips, dovetails) so magnets provide retention, not the entire structural load.
If you’re near motors or drivers, consider temperature-coded grades (H/SH) for consistency.
Outdoor Projects
Don’t ignore coating. Humidity combined with scratches and time can turn a strong magnet into a flaky mess.
Nickel-coated magnets are common, but if you expect abrasion, consider designs that shield the magnet (thin cap, recessed pocket, or sleeve).
Step 4: Don’t Pick a Magnet Grade in Isolation: Pick a Magnetic Setup
This is where makers level up fast. Instead of “a magnet,” think of a magnetic circuit or a magnetic assembly.
A magnet backed by steel can feel dramatically stronger than the same magnet floating in plastic. Likewise, a magnet sitting flush against a target plate performs better than one separated by a millimeter of air gap.
If you’re building latches, mounts, clamps, or fixtures, it’s often easier to choose from proven magnetic assemblies rather than reinventing the mounting hardware from scratch. (That phrase is also a useful search term when you’re trying to avoid fragile glue-only setups.)
Step 5: A Simple “Grade Picker” You Can Keep in Your Notes
Use this as a quick starting point:
General indoor builds, tight fit: Start around N35-N42.
Small magnet, needs more bite: Consider N42-N52.
Near heat/sun/motors: Look for H/SH variants first, then pick size/grade.
Load in shear (sliding): Design the pocket/mechanics first. Don’t rely on grade alone.
Corrosion risk: Protect the magnet with a recess, cap, or enclosure.
Frequently Asked Questions
Do I always want the highest grade, like N52?
Not always. N52 looks impressive, but it’s not always the best option. A slightly larger N35 or N42 with a clean steel target and almost no air gap can feel stronger in real use than a tiny N52 stuck behind paint and plastic. If space isn’t tight, size and mounting usually give you more of an advantage than chasing the absolute top grade.
Why does the magnet feel weaker once it’s inside my project?
Because the product photo is lying to you a little. Pull tests are usually done with a big, flat steel plate and no gap. In real life, you’ve got paint, plastic, tape, misalignment, or a small contact patch. Every bit of extra distance and every rough surface eats into the pull. When in doubt, plan for that gap and compensate by increasing the size or number of magnets.
Will strong magnets mess with my electronics or cards?
They can, depending on how close you get. Dragging a bare magnet across a PCB, hard drive, or magnetic strip is asking for trouble. A magnet sitting a few centimeters away in a housing is usually fine. As a rule of thumb, don’t park big neodymium magnets on top of drives, sensors, or anything with a stripe or chip you rely on.
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