Dimensional tolerances for tubes and rods — how to understand them (PC / Acrylic XT / Acrylic Cast)
Catalog (nominal) dimensions are only a reference point. In real production, plastic tubes and rods always have permissible deviations — and these tolerances determine whether a part will fit correctly in fittings, holders, sockets, bushings, or seals (e.g. O-rings).
Dimensional tolerances for tubes and rods — how to understand them (PC / Acrylic XT / Acrylic Cast)
Catalog (nominal) dimensions are only a reference point. In real production, plastic tubes and rods always have permissible deviations — and these tolerances determine whether a part will fit correctly in fittings, holders, sockets, bushings, or seals (e.g. O-rings).
For many polymers, tolerances are given as a percentage, meaning the allowable deviation in millimeters increases with the size.
How to calculate a percentage tolerance in mm?
- ± 1% → deviation = nominal dimension × 0.01
- ± 2% → deviation = nominal dimension × 0.02
Examples:
- Ø 100 mm with ± 1% tolerance → ± 1.0 mm
- Ø 200 mm with ± 2% tolerance → ± 4.0 mm
Dimensional tolerances for polycarbonate (PC) tubes
Polycarbonate (PC) is a material with very good mechanical and optical properties. To ensure high repeatability in assembly, the allowable deviations are listed below.
1) Outer diameter (OD) tolerance
Outer diameter range | Tolerance |
|---|---|
from Ø 7 mm to Ø 150 mm | ± 1.0 % |
from Ø 160 mm to Ø 300 mm | ± 2.0 % |
2) Inner diameter (ID) tolerance
Inner diameter range | Tolerance |
|---|---|
from Ø 7 mm to Ø 150 mm | ± 1.5 % |
from Ø 160 mm to Ø 250 mm | ± 2.5 % |
3) Wall thickness tolerance
Tube diameter (Ø) | Wall thickness tolerance |
|---|---|
from 7 mm to 64 mm | ± 5 % |
from 70 mm to 100 mm | ± 8 % |
from 110 mm to 200 mm | ± 10 % |
from 220 mm to 250 mm | ± 15 % |
Dimensional tolerances for extruded acrylic (XT) tubes
Extruded (XT) tubes have different tolerance characteristics than cast (GS/Cast) tubes. The data below refers to the extrusion process.
1) Outer diameter (OD) tolerance
Outer diameter range | Tolerance |
|---|---|
from Ø 7 mm to Ø 150 mm | ± 1.0 % |
from Ø 160 mm to Ø 300 mm | ± 2.0 % |
2) Inner diameter (ID) tolerance
Inner diameter range | Tolerance |
|---|---|
from Ø 7 mm to Ø 150 mm | ± 1.5 % |
from Ø 160 mm to Ø 300 mm | ± 2.5 % |
3) Wall thickness tolerance
Tube diameter (Ø) | Tolerance |
|---|---|
from 7 mm to 64 mm | ± 5 % |
from 70 mm to 100 mm | ± 8 % |
from 110 mm to 200 mm | ± 10 % |
from 220 mm to Ø 300 mm | ± 15 % |
4) Cut length tolerance
Standard length tolerance: ± 1.0 mm
Dimensional tolerances: cast acrylic (Cast) tubes
Cast acrylic (Cast) tubes offer very good optical quality. Due to the casting process, tolerances may be different — including asymmetric tolerances for the outer diameter.
1) Outer diameter (OD) tolerance — asymmetric
Outer diameter range | Tolerance |
|---|---|
from Ø 50 mm to Ø 100 mm | • 1.0% / - 1.5% |
from Ø 110 mm to Ø 500 mm | • 1.0% / - 1.5% |
2) Wall thickness tolerance
Wall thickness | Tolerance |
|---|---|
3 mm | ± 20 % |
4 mm | ± 15 % |
from 5 mm to 15 mm | ± 20 % |
3) Cut length tolerance
Standard length tolerance: ± 1.0 mm
OD calculation example: for a Ø 200 mm tube, the permissible size can range from 197 mm (-1.5%) to 202 mm (+1%).
Dimensional tolerance specification for rods (round and square)
1) Round rods — diameter tolerance
Diameter range (Ø) | Dimensional tolerance |
|---|---|
from 2 mm to 30 mm | ± 0.1 mm |
from 32 mm to 60 mm | ± 0.3 mm |
from 65 mm to 200 mm | ± 0.5 mm |
2) Square rods — side tolerance
Side dimension | Dimensional tolerance |
|---|---|
from 6 mm to 30 mm | ± 0.3 mm |
from 35 mm to 60 mm | ± 0.5 mm |
from 65 mm to 200 mm | ± 1.0 mm |
3) Cut length tolerance
Length tolerance: ± 2.0 mm
FAQ
Can I order an “exact” specific size?
In practice, tolerances always apply. For tight fits, consider a design allowance or finishing machining.
Which dimension is critical: outer Ø or inner Ø?
It depends on the application: external fit (OD) vs insert/flow (ID).