Da Inglese a Italiano Tecnico/Meccanico Meccanica/Ingegneria meccanica gas cylinders

It is basically a Dewar flask for cryogenic liquids, but I don't know how to provide a non-misleading translation for "loose fitting":
"3.9.7 Cryogenic Liquids:
3.9.7.1 Use special vacuum jacket containers with loose fitting lids to handle small quantities. Vacuum jacketed containers provided by the gas supplier have overpressure relief devices in place.
3.9.7.2 Fill containers with cryogenic liquids slowly to avoid splashing. "