The aluminium caps are so designed that the oher layered caps,or the center of single-layered caps,can be removed to expose the center of the rubber closure without disturbing the bandthat holds the closure in the container.rubber closures for use with intravenous administration sets often have a permanent hole through the closure. In sush cases, a thin rubber disk overlaed with a solid aluminium disk is placed between an inner and outer aluminium cap, thereby providing a seal of the hole though the closure.
Single-layered aluminium caps may be applied by means of a hand crimper known as the fermpress .double- or triple- layered caps require greater force for crimping ; therefore,heavy-duty mechanical crimper are required.
A relatively recent trend, although now standard practice, is the requirement that sealing of vial and other container be accomplished in class100/grade A/ISO 5 clean room environment. Formerly sush sealing occurred in unclassified environments