Most magnet sourcing failures trace back to one cause: a vague specification. Here is a simple checklist that covers everything a supplier needs, in the order that works.
The five-question checklist
- What must it do? Holding, torque, sensing or shielding? State the required force or flux — this decides size and material.
- What temperature will it see? The most commonly forgotten question, and the most damaging: the wrong grade can permanently lose its magnetization in a hot motor. Give the worst-case temperature, not the average.
- What shape and size? Provide a drawing with dimensions and tolerances, and mark the magnetization direction on it — a perfect part magnetized the wrong way is useless.
- What grade and coating? Name a grade if you know it, but also state Br and Hcj so suppliers can't interpret the name differently. Specify the coating — nickel is the default, zinc and epoxy common — and the environment decides which you need.
- What is the budget and schedule? Standard shapes and grades are often stocked; custom parts need new tooling. Order early for urgent programs.
"N42" is not a spec
Suppliers interpret grade names differently, so two quotes for "N42" can cover different strength windows. Always add Br and Hcj limits — and never compare magnets by surface gauss, which depends on shape and probe position.
Common mistakes
- Choosing the coating after the design is frozen — plating adds thickness.
- Forgetting the magnetization direction — put it on the drawing.
- Ignoring the temperature environment — an N-series magnet in a 150 °C motor will fail.
- Comparing quotes on vague specs — different grade windows and test methods are not comparable bids.
One drawing beats ten phone calls: a complete RFQ gets you comparable quotes and a part that works the first time.
Read on: what to include in a magnet RFQ → · why magnets hate heat →