de 102007009082 the actuator pin 40 also presents a longitudinal groove 44 facing in the direction of the spring 33 adapted to allow insertion of the probe of a test device for making electrical measurements as described in the aforesaid patent application it mi2012a001974 granted on mar 3 2015 as it1414636 the substantial differences of the connecting device according to the present invention with respect to the one described in the document de 102007009082 which allow to reduce the inner transverse bulk of the device and then to obtain an increase of the density of connection elements in case of multi pole terminal blocks or plug connectors consist in the fact that in correspondence of the said hollow 42 formed in the actuator pin 40 two tapers or indentations 45 of the flanks of the pin are provided bounded by an intermediate ribbed part preferably central 46 best seen in fig3 c and said leg like ascending portion 35 of the spring 32 has a corresponding window or groove 39 adapted to receive said ribbed portion 46 of the actuator in closed clamp conditions at rest without conductor as shown in fig4 a and 4 b in this rest condition the housing of the ribbed part of the actuator 46 in the window 39 of the spring and the housing of the solid parts 39 u2032 delimiting the window 39 in the corresponding tapered sides 45 of the actuator allow the complete extension of the spring according to an alternative embodiment.