The SPI mould classes describe how long an injection mould is expected to run: Class 101 for more than a million cycles, down to Class 105 for prototype moulds of a few hundred parts. The class sets expectations for steel, hardness and construction, so specifying it helps suppliers quote comparable tools.
The five classes
| Class | Typical cycle life* | Use | Typical construction |
|---|---|---|---|
| 101 | More than 1,000,000 cycles | Very high production | Hardened steel cavities and cores, hardened mould base, the highest price |
| 102 | Up to 1,000,000 cycles | Medium to high production, abrasive resins or tight tolerances | Hardened cavities and cores, strong mould base |
| 103 | Under 500,000 cycles | Medium production | Pre-hardened steel such as P20 for cavities and cores |
| 104 | Under 100,000 cycles | Low production, non-abrasive resins | Mild steel or aluminium |
| 105 | Under 500 cycles | Prototypes | Low-cost materials, e.g. aluminium or cast metal |
* Typical values from the SPI (now Plastics Industry Association) classification; the full standard also covers details such as cooling, guiding and ejection.
How to choose a class
- Start from the total number of parts over the product’s life, not one year’s order.
- Glass-filled or abrasive resins push you towards Class 101 or 102 even at moderate volumes.
- For design validation, a Class 105 mould – or CNC prototypes and vacuum casting – may be enough.
How this relates to our moulds
We build production moulds for 50,000 to 1,000,000 shots and state the expected life in every quotation, together with the steel grade, hardness and mould base. If your specification calls for an SPI class, tell us when you request a quote and we will match steel and construction to it. The steels behind each class are compared in our mould steel selection guide, and their effect on price in injection mould cost.
Frequently asked questions
Is a higher mould class always better?
No. A Class 101 mould costs much more than you need for a product that will sell 50,000 units. Choose the class that matches your total volume and resin.
Do Chinese mould makers use SPI classes?
Many buyers specify them, and we can quote to the class you need. Steel, hardness and expected life are written into the quotation in any case.
What is the difference between Class 102 and 103?
Class 102 moulds use hardened cavities and cores for up to about a million cycles; Class 103 moulds typically use pre-hardened steel such as P20 for medium production of under 500,000 cycles.
Have a part to discuss? Send your drawing or 3D file through our inquiry form – our engineers reply with a quotation and DFM suggestions.