This data-set was collected as part of the experimental validation of a Jacobian-based stiffness analysis for parallel manipulators with non-redundant legs. The dataset is stored as a tab-delimited ASCII file. The dataset consists of spatial wrench measurements (6-dimensional vectors containing a moment vector, [m_x, m_y, m_z], and a force vector [f_x, f_y, f_z]) over the workspace of a spatial, 1-DoF, 3-RRR mechanism. The data set consists of six subsets of measurements, where each subset is marked by a letter in the first column. Each subset consists of five arrays, where the first array describes the wrench measurement at a reference pose, followed by four arrays that describe the planar wrench measurements at a 5 mm displacement along the X-axis, a 5 mm displacement along Y-axis, a 5 mm displacement along Z-axis, and a rotation of 1/8 rad about the Z-axis respectively. The pose of the mechanism was set manually, using