Spring Scales, Pull-type, 250-g/2.5-N, Package of 6. Recommended or required for Coefficient of Friction—Advanced Inquiry Laboratory Kit (Catalog No. AP7725), Archimedes’ Principle and Buoyancy—Advanced Inquiry Laboratory Kit (Catalog No. AP7995), Force and Motion—Super Value Laboratory Kit (Catalog No. AP6929) and Simple Machines—Student Laboratory Kit (Catalog No. AP6931).