A test tube brush is used to clean residue and stains from the interior surfaces of narrow openings like test tubes ensuring they are free from contaminants and ready for precise experiments or use. Its specialized design, with a sturdy wire handle and bristles, allows for effective cleaning of delicate glassware without damaging the inner surfaces. 

 * Removing Residue: The brush effectively removes sample residue, stains, and contaminants that may remain stuck to the inner walls of the glassware. 

 * Maintaining Sterility and Accuracy: Thorough cleaning is crucial in laboratories to prevent cross-contamination between experiments and to maintain the accuracy of measurements and experimental results. 

 * Variety of Sizes: Brushes are available in a wide range of diameters to accommodate different sizes of tubes and glassware, ensuring an efficient fit and effective cleaning.