Screw cap,known as Continuous Thread Closure,size are generally expressed as two numbers.The first number refers to the cap diameter(in millimeters). The second number refers to the height and thread configuration of the closure or finish.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.