This Kimble® Erythrocyte Sedimentation Rate (ESR) tube rack features leveling bubbles and adjustment screws allowing tubes to be held firmly in a perpendicular position ensuring accurate readings. They also help reduce the chance of bio hazardous contamination by preventing accidental spills. Designation: For Westergren and Wintrobe Tubes. Capacity: Six Tubes. Per Each. Kimble® #: 2212N.