At least four criterions/methods to measure mechanical effects of electoral systems can be distinguished: measuring disproportionality, the reduction in number of parties, the party advantages and the threshold percentages. In this manuscript we focus on the thresholds. We first concentrate on a description of legal, theoretical, and empirical thresholds as measures of mechanical effects. Further, we analyse the relationship between (the natural logarithm) of district magnitude and the empirical threshold and between the empirical threshold and the effective number of parties. As starting point we take districts in Spain, Portugal and Hungary as the level of analysis. We clearly show that there is a negative causal connection between district magnitude and the threshold percentage and between threshold percentage and the number of parties.