This is a detail up parts for plastic models and figures.Can be used for multi purposes with your creativity.Set of 20S size- Outer diameter 3.1mm Width 2.5mm- Inner diameter 2.1mm Compatible spring 1.9 / 2.0mm- Brass-plated * Reference length when connecting 20 pieces (gap 0.4 mm) 57 mmM size- Outer diameter 4.2mm Width 3.5mm- Inner diameter 3.1mm compatible spring 2.9 / 3.0mm- Brass plated * Reference length (gap 0.8mm) 85mm when connecting 20 piecesL size- Outer diameter 5.2mm Width 4.5mm- Inner diameter 4.1mm compatible spring 3.9 / 4.0mm- Brass-plated * Reference length when connecting 20 pieces (gap 0.8 mm) 105 mm*This set comes with only metal parts, strings(Springs) for connecting are not included.