Needak Springs are 4.25″ in length.
They are available for Soft Bounce and Hard Bounce Rebounders.

4.25″ – Needak Soft Bounce
Set of 6 –  $28.95
Set of 36 – $90.00

4.25″ – Needak Hard Bonce
Set of 6 –  $37.95
Set of 36 –  $125.00

Classic Springs – 3.5″
Set of 6 –  $22.95
Set of 36 – $74.95