Centrifuge Tube, Test Tube Rack for 10, 15 and 50 Ml Tubes Plastic rack for 10, 15, or 50 ml tubes. Fit test tubes or centrifuge tubes. 20 holes for 50 ml tubes (hole diameter 1 1/8", 28 mm). 30 holes for 10/15 ml tubes (hole diameter 5/8", 15 mm). Easy assemble.