A weld gun having a linkage, which relates pivotal motion of a pair of laterally opposed facing electrodes of the weld gun in a predetermined manner. A square neck of a bolt fits into an oblong hole in a component and prevents the bolt from turning. When the regression analysis model and the number of shots to be measured are determined in advance, a method is used for determining an optimal number of shots to be measured according to the regression analysis model and process dispersion using a confidence interval estimating method. The pivot arm assemblies are mounted to the base frame substantially laterally opposed to each other through the link and first pivot arm such that the pivot arm assemblies are independently pivotable relative to the base frame. The bigger diameter end of the sprinkler head is coupled with the support structure.