Versilic silicone. Translucent. Secure seat, pleasant to handle. The caps are actually produced with a slightly smaller inner Ø and therefore offer a very secure seat. - Type number corresponds to outer Ø of the test tube or vessel to be closed (glass, plastic, metal). Versilic silicone. Translucent. Secure seat, pleasant to handle. The caps are actually produced with a slightly smaller inner Ø and therefore offer a very secure seat. - Type number corresponds to outer Ø of the test tube or vessel to be closed (glass, plastic, metal).