Strands: Concentric strands

In concentric strands, the individual wires are subject to an exact positioning around a core wire, which ensures an all-out uniform structure.


  • Extrusion: thin-gauge coating with high-grade isolation materials
  • 7-end strands are particularly suited for data cables with high frequencies of transmission

Particular benefits for our customers

  • Uniform elongation of single wires
  • Low tolerances, even in single wires (even outperforming ASTM)

Manufacturing range

  • Materials: Cu-ETP1 and Cu-OF1
  • Bare, tin-plated, nickel-plated, silver-plated
  • Left-hand lay or right-hand lay
  • Variation: soft annealed
  • Single-wire diameter: ranging from Ø 0.05 mm to Ø 0.51 mm
  • Cross-section: ranging from 0.02 mm2 to 630 mm2


The following strand constructions are possible:

concentric strand 7 end
concentric strand 19 end
concentric strand 37 end

7 ends = 1 + 6
19 ends = 1 + 6 + 12
37 ends = 1 + 6 + 12 + 18
More relevant details can be found in ASTM regulation B 354.

7-end and 19-end strands are the preferred choices for cables used in electronics. The precise positioning of the individual wires makes for a smooth and even surface as well as an unvarying diameter.

In concentric strands with more than 7 wires, 4 different lay-driven sub-categories can be found:

Construction unilay

Unilay concentric

  • same lay direction
  • same lay length
  • manufactured in one working step
  • nearly round construction (hexagonal)

Unidirectional concentric

  • same lay direction
  • different lay lengths for each working step
  • manufactured in two working steps
  • more round than unilay concentric

Direction of stranding

Construction true concentric

Equilay concentric (reversed lay stranding or SZ stranding)

  • different lay directions
  • same lay length
  • manufactured in two working steps
  • very round construction

Conventional concentric

  • different lay directions
  • different lay lengths for each working step
  • manufactured in two working steps
  • very round construction

Direction of stranding

Reversed lay direction / SZ stranding

S ➔ left hand lay

Z ➔ right hand lay

Strands with the same lay direction are generally called unilay.

Strand with opposing lay direction (SZ stranding) are called true concentric.

The roundness of a strand is driven by its lay length as well:

longer lay length = hexagonal

shorter lay length = more round

Moreover, there is a patented manufacturing process that allows for the production of strands featuring a highly compact and precise round structure: LEONI’s smooth bunches


Reel sizes from 80 mm (1 kg) to 630 mm (400 kg), subject to diameter

Packaging information

Other dimensions and materials

You need special designs and products for your applications?

Our R&D team is your partner for customised solutions.

Please contact!

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