Abstract: An electrical spring probe has an elongated contact and a helical spring. The spring probe is mounted in a through hole of a non-conductive substrate. The elongated contact includes a head with a V-slot groove for engaging a solder ball lead of an IC package, a shoulder providing a surface to retain a helical spring and a beam for providing a short contact path through the spring. The helical spring is disposed about the contact, with contiguous coils on each end. The upper end of the spring is secured to the contact shoulder immediately under the head. The middle coils of the spring have a larger diameter than the contiguous coils on either end to retain the spring probe assembly in the non-conductive substrate. The bottom end of the helical spring has contiguous coils some of which extend below the substrate surface to make electrical contact with a printed circuit board. The bottom contiguous coils are of a reduced diameter and have a center axis offset from the main axis of the spring probe assembly.