Rubber Tolerances

All the good stuff about rubber – its flexibility, elasticity, its malleability and fact that the material can flow into complex, unusual shapes during moulding – also means that it is inevitably more difficult to control than other materials.

All elastomers shrink during the moulding process, and the extent to which that happens will vary depending on not only the material itself, but also on the tool design, moulding method, geometry of the product and hardness of the compound.

One of the key factors in creating a consistent, repeatable product lies in selecting the right compound and designing the tool to produce the critical areas of the finished article to a consistent standard. This means making sure we understand from the outset what is most important to you, and which areas (the sealing faces of a seal, the customer-facing areas for an aesthetic product) are your priority.

There are standard tolerances within which we work, but if we don’t know in advance that a particular aspect of a part is critical, we may not factor that into the design or the processes. Collaboration to establish an agreed standard is key.

For a general guide, see below (downloadable pdf beneath). This information is provided for general guidance only, please contact us to confirm any specific requirements .

Rubber Moulding

Linear Dimensions (BS ISO 3302-1)

Nominal DimensionsClass M1Class M2Class M3Class M4
aboveup to and includingF & C±

F = Fixed dimensions; dimensions created by features on the same part of the tool

C = Closure dimensions; dimensions that are created across two mating parts of a tool and therefore more prone to variation.

All values in millimetres unless otherwise stated


Hardness tolerance variation from nominal

Shore A            =          ± 5°

IRHD                =          ± 5°


Cross-sectional dimensions (BS ISO 3302-1, E2)

Range0 – 1.51.5 – 2.52.5 – 4.04.0 – 6.36.3 – 1010 – 1616 – 2525 – 4040 – 6363 – 100
Tolerance ±0.250.350.400.500.700.801.001.301.602.00

Range = Above – Up to and including. All values in millimetres unless otherwise stated

Machined Rubbers & Plastics

Linear Dimensions (DIN ISO 2768-1 m)

0 – 6mm                        =          ± 0.10mm

6 – 30mm                      =          ± 0.20mm

30 – 120mm                   =          ± 0.30mm

120 – 400mm                 =          ± 0.50mm

400 – 900mm                 =          ± 0.80mm

Hardness tolerance variation from nominal:

Shore A            =          ± 5°

IRHD                =          ± 5°


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