Pad-cap retainer rings hold neoprene pads that fit onto the ends of concrete test cylinders. Made from plated high-alloy steel to resist rust and deformation fatigue. Bearing surfaces machine-planed to within 0.002". Supplied two per set. Neoprene pad inserts are made from a tough elastomeric material that evens out and fills irregularities in the ends of concrete cylinders to assure even distribution of test loads for consistent results.