Sizes · diameters, tolerances, shafts

Plastic core sizes and tolerances

ROLL Lab · updated 24 October 2026 · sources at the bottom of the page

Diameters: inches and millimetres

The roll world thinks in inches; European plants produce in millimetres. The most common nominal sizes:

Alongside inches there are many intermediate metric sizes (for example 70, 80, 90, 100, 128, 150 mm), tied to specific machines. Because a plastic core is extruded through a die and a sizing sleeve, it can be made in almost any diameter, but each new size needs tooling: ask the supplier which sizes it already has.

Walls range from 1–2 mm for tape cores to 12–15 mm for heavy rolls. The outside diameter equals the inside diameter plus twice the wall, and it matters for the starting diameter of the roll and for plugs.

Inside diameter tolerances

ISO 13542 sets internal diameters and tolerances for paper and board reel cores. It does not cover plastic, but it is the reference most used in specifications because it describes the same interface: core and shaft. Tolerances are plus-only, because a core narrower than nominal will not fit.

Source: ISO 13542:2006, Table 1. Extruded and sized plastic cores can sit well within these values: with plain shafts without expansion, buyers often ask for tolerances of a few tenths of a millimetre. The tighter the tolerance, the more production and inspection cost.

Ovality, wall and concentricity

Ovality. ISO 13542 defines it as the difference between two perpendicular inside diameters: no more than 0.5 mm below 70 mm and 1.5 mm from 70 mm upwards. On the shop floor the average of two readings at 60° with a three-point bore micrometer is also used: it is a different method, not to be confused with the first.

Practice values for plastic. The GMP quality control procedures in Fiaptech technical documentation (a company with corporate ties to ROLL) give roundness limits for the outside diameter, calculated as the difference between two readings:

Wall uniformity. The same source measures centring as the difference between maximum and minimum wall over four readings: at most 0.2 mm for walls under 5 mm, 0.3 mm between 5 and 9 mm, 0.4 mm between 9 and 15 mm. An uneven wall makes the roll run eccentric and weakens the thinnest point.

Straightness and TIR

For long cores and fast winding, the core must be straight and run true. Two quantities:

• Bow: the maximum deviation of the axis from a straight line, in mm per metre of length. It is measured with the core on a surface plate or on two supports.
• TIR (total indicated runout): the swing read on a dial indicator while the core turns on two V-blocks or on a shaft. It sums up ovality, wall eccentricity and bow.

There are no standard values for plastic cores. The value is agreed with the customer starting from line speed and how sensitive the material is: for fast winding of thin films, a few tenths of a millimetre is typical. Asking the supplier how it measures TIR (on which supports, how far from the ends) avoids arguments.

Mind the temperature: a long core stored with one side in the sun bends. Straightness measured at the factory may not be what reaches the machine.

Length and ends

Length tolerances depend on the cutting method: automatic machines usually claim precision between ±0.1 and ±0.3 mm. Checking a tolerance needs an instrument with a much finer resolution: a tape measure reads 1 mm and is not enough to check ±0.3 mm; you need a caliper or a gauge with an end stop. On shafts with many cores side by side, tolerances add up: ten cores at +0.5 mm make 5 mm.

Ends can be left as cut, deburred or chamfered, or given notches for drive dogs. A deburred end avoids chips on the material and makes it easier to slide onto the shaft. Cutting plastic cores.

Smooth or ribbed bore

• Smooth: the standard. It suits most air shafts and is easier to clean.
• Fine ribbed: thin longitudinal ribs that increase friction with the shaft lugs. Useful with high torque and slippery films.
• Deep ribbed: more pronounced ribs for friction shafts, or when the core must transmit torque without strong expansion.
• Trade names: catalogues call a ribbed bore grooved, serrated, fluted or knurled, depending on how many ribs it has and how fine they are. These are not standard terms: in the specification state the number, depth and profile of the ribs.

Ribs make the core a little harder to wash and can trap dust: clean areas prefer a smooth bore.

Shafts and chucks: what the core works with

The shaft is chosen with the machine builder. Plastic cores, harder than cardboard, mark less under the lugs but can slip if the surface is too smooth and the torque high.

How to measure: tools and sampling

Source of the sampling: GMP procedures in Fiaptech technical documentation, adapted by the ROLL Lab. Incoming inspection and specification.

Try it with your own data below; method, assumptions and sources are on the dedicated page: the plastic core weight calculator.

Frequently asked questions

Further reading

Sources

1. ISO 13542:2006, Paper and board — Specification for internal diameters of cores for reels (Table 1 and ovality)
2. ISO 11093-4, measurement of core dimensions
3. Fiaptech technical documentation, GMP quality control procedures (a company with corporate ties to ROLL): roundness, wall uniformity, sampling
4. Fiaptech technical documentation, Smart Book “Which core?”: bore finishes, ends, shafts
5. D. Van Hove, “Radial approach for the design of cores in film applications” (bore measurement with a three-point micrometer)
6. ROLL Lab analysis