This data-set was collected as part of the experimental validation of a Jacobian-based stiffness analysis for parallel manipulators with two end-effectors and non-redundant legs. Measurements have been performed over the workspace of a passive planar 4-DoF mechanism with two end-effectors. The mechanism has four RPR legs, which are connected to the base, while in addition two RRR chains internally connect the two end-effectors and the terminal links of the three legs. The mechanism is described as 4-DoF, because rotation of both end-effectors is not considered. This rotation is free due to the collocation of joints at the end-effector, which means that no moments can be applied on the end-effectors by the mechanism. Rotation was therefore not considered in the analysis. The dataset is stored as a tab-delimited ASCII file. The dataset consists of planar force measurements on both the first end-effector (EE1) and the second end-effector (EE2). As such, the …