These Wilmad-LabGlass standard 5 mm NMR tube caps come in a package of assorted colors. The different colors help track samples based on various reference solvents. These caps are compatible with 5 mm OD NMR tubes and are available in either an assortment pack of 100 or 1000 caps. When using chloroform or acetone as a reference solution, avoid direct contact between the sample and cap and long-term storage over two hours.