Using with Kuderna-Danish evaporation equipment,they use Keck clamps rather than spring hooks to attach to flasks,have an air jacket around the tip to reduce the risk of the sample boiling dry. ● Material:borosilicate glass ● Color:Clear ● High temperature resistance,corrosion resistance,chemical resistance ● 4ml and 10ml tube lenght is 100mm ● 25ml tube lenght is 170mm ● Joint size 19/22:19 refers to joint diameter,22 refers to joint height,other specifications and so forth ● Matched with KUDERNA-DANISH Flasks