Bel-Art F18745-1300 Switch-Grid Test Tube Rack Grid; 10-13mm, Orange (Pack of 4) Switch-Grid Test Tube Rack system is more compact and less expensive than purchasing multiple racks Switchable grids allow user to utilize two tube sizes in one rack; change grids in one side or both (2 grids needed per side) Orange grids fit 10mm to 13mm tubes