Valid passport required by all. Visas may be used for travel to the USA until the date it expires or if marked 'valid indefinitely' for up to 10 years.
Some visas are valid for multiple entries.
The length of stay in the USA is determined by US immigration officials at the time of entry, but is generally 6 months. Any new visa issued will be valid for a maximum of 10 years. The embassy will provide a paying-in slip. The fee must be paid in cash at a bank prior to submitting a visa application to the US Embassy. In the UK, Barclays Bank does not charge a handling fee for this service.