Abstract: This invention relates to a spring fastener, which comprises engagement springs in opposite sides of the fastener. Each engagement spring has an engagement region comprising a hindrance portion, which increases considerably the removal to insertion force ratio as compared to such ratio in the absence of the hindrance portion, thus permitting very easy insertion with considerably more difficult removal of the fastener from the slot of a panel, which provides an efficient ergonomically balanced removal to insertion force ratio. The hindrance portion comprises ripples or other hindrance elements of unexpectedly minute dimensions for providing this efficient ergonomic force balance. The combination of the above structures with the presence of barbs being bent at their front portion improves immensely the ergonomic character of the devices.