Spring core for a mattress

A spring core for a mattress, comprising a plurality of identically configured helical circular springs each made of a single piece of wire having a central spiral position (15,16) defining a spring axis (17) and terminating at opposing ends with upper and lower end spirals (11,31) disposed in planes substantially perpendicular to said spring axis, said springs being arranged in side by side rows and connected with each other at said upper and lower end spirals (11,31) by connecting elements (30) arranged in said planes, said upper and lower end spirals (11,31) each being substantially U-shaped and having a longer leg (12) and a shorter leg (13) connected to each other by a base web (18), said legs (12,13) of each end spiral being laterally outwardly spaced from said central spiral portion in relation to said spring axis, the radial spacing between said longer leg (12) and said central spiral portion (15,16) being greater than the corresponding spacing between said central spiral position and said associated shorter leg (13) of the same end spiral (11,31), the opposing end spirals of each spring being rotated approximately 180 degrees in relation to each other to dispose the longer and shorter legs of the upper end spiral of each spring in mirror symmetry to the longer and shorter legs, respectively, of the associated lower end spiral.