Updated through August 2026.
Classic K’NEX includes several flexible parts used to store energy, maintain tension, transfer movement or operate mechanisms. These include rubber bands, a Flex Band and string.
Although these parts may look simple, their size, thickness and type can affect how a model works.
Rubber Bands
K’NEX rubber bands were supplied in different sizes, thicknesses and colours. Depending on the model, they can provide tension, return movement or stored mechanical energy.
They are used in applications such as moving mechanisms, rubber-band-powered models and some launcher or slingshot arrangements.
| Part number | Colour | Size / type |
|---|---|---|
| 92005 | Brown | 76 mm |
| 92013 | Blue | 102 mm |
| 92013B | Brown | 102 mm |
| 92001 | Brown | 185 mm / 7¼ in.; heavy duty |
| 92002 | Red | Rubber Band |
| 92008 | Black | Thick Rubber Band |
| 92010 | Black | Thin Rubber Band |
The size and thickness of a rubber band affect its behaviour under tension. A similar-looking replacement is therefore not necessarily equivalent to the original K’NEX part.
Flex Band
The translucent 3055001 Flex Band is identified separately from the conventional K’NEX rubber bands.
| Part number | Colour | Type |
|---|---|---|
| 3055001 | Translucent | Flex Band |
It should not automatically be treated as simply another size of ordinary rubber band. The 3055001 Flex Band is associated with K-Force and is included here as a flexible K’NEX part rather than as a conventional rubber band.
String
String is used where movement or force needs to be transferred over a distance. Common applications include pulleys, cranes, lifting mechanisms and other moving constructions.
| Part number | Colour | Length / notes |
|---|---|---|
| 92004 | Black | approx. 1 m |
| 92135 | Black | approx. 1 m |
| 92003 | White | approx. 1.8 m |
| 920041 | Red | approx. 3.5 m |
Both 92004 and 92135 are documented as separate K’NEX string part numbers. They should therefore not be assumed to be the same part solely because both are known as black string of approximately the same length.
Rubber Bands as a power source
A stretched or twisted rubber band stores mechanical energy. When released, that energy can be converted into movement.
K’NEX models have used this principle for several purposes, including rubber-band-powered models and launching mechanisms. In some slingshot-type launchers, an elastic component provides the stored energy used to propel the moving part.
The launcher itself remains a separate mechanism; the rubber band is its energy-storing component.
String and pulleys
String can be combined with K’NEX pulleys to lift or lower parts, transfer pulling force and change the direction in which that force acts.
This makes it particularly useful in cranes, lifts and other mechanical constructions.
Pulleys themselves remain part of the K’NEX Wheels, Tyres, Hubs & Pulleys family. They are mentioned here because pulley systems are one of the principal applications of K’NEX string.
Identification
When identifying a loose K’NEX band or piece of string, consider its part number, colour, original length, thickness and application.
Length alone is not always sufficient. Different documented part numbers may describe parts with apparently similar dimensions.
Safety
Strings and elastic bands should be used in accordance with the age recommendations and safety instructions for the original K’NEX model.
Rubber bands deteriorate with age. An elastic band that has become brittle, cracked, stretched or otherwise damaged should not be used under tension.
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