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, Cu-OF1 and LEONI Histral® alloys
  • 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

7-end = 1 + 6

concentric strand 19 end

19-end = 1 + 6 + 12

concentric strand 37 end

37 end= 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.

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