Common screw closures (from left to right): Plastic bottle with plastic screw cap, Dispensing closure for salad dressing (with inner seal), Break-away closure for syrup, Dispensing pump closure, Dispensing closure (with inner seal), Spray pump, Metal closure on glass jar, Child resistant closure, Cap on toothpaste, Measuring cap
A "sports cap", which appears on many water bottles, seen in closed configuration at left and in open configuration at right, allowing the water to pass around the central blue piece.
A screw closure is a mechanical device which is screwed on and off of a "finish" on a container. Either continuous threads or lugs are used. It must be engineered to be cost-effective, to provide an effective seal (and barrier), to be compatible with the contents, to be easily opened by the consumer, often to be reclosable, and to comply with product, package, and environmental laws and regulations. Some closures need to be tamper resistant and have child-resistant packaging features. A tamper-evident band is a common tamper warning for screw caps of bottles, for example.
Screw caps' use as an alternative to cork for sealing wine bottles is gaining increasing support. A screw cap is a metal cap that screws onto threads on the neck of a bottle, generally with a metal skirt down the neck to resemble the traditional wine capsule ("foil"). A layer of plastic (often PVDC), cork, rubber, or other soft material is used as wad to make a seal with the mouth of the bottle.
Sake bottles are almost universally closed with screw caps (some are packed in barrels, or novelty bottles).