Sprol

Enrichment is a process that uses networks of machine centrifuges, which spin uranium hexafluoride gas into low-enriched uranium for civilian power plants and highly enriched uranium for nuclear weapons fuel, depending on the duration of the process.
National Public Radio

Iran said it successfully enriched uranium using 164 centrifuges. For large-scale enrichment, Iran needs tens of thousands of centrifuges.

Iran’s nuclear boss, Gholamreza Aghazadeh, said Iran aims to expand the process to use 3,000 centrifuges in the last quarter of 2006, meaning Iran is preparing for a semi-industrial scale enrichment.

The centrifuge program is located at the Natanz Uranium Enrichment Plant, parts of which have been built underground to protect it from air or missile strikes.

It is not clear whether reaching the 3,000 mark means building more centrifuges. In 2005 – when Iran had suspended enrichment-related activities – Iranian officials said the country had around 2,000 centrifuges.
Seattle Post-Intelligencer

Uranium enrichment is the greatest technical obstacle to a country making nuclear weapons — or even fuel for reactors, which Iran says is its sole aim. It requires precision-crafted centrifuges made out of hardened steel, which must spin very fast without crashing. Once uranium has been enriched to the level needed by a reactor, it takes about as long again to enrich it to weapons grade.

Hojatoleslam Ali Akbar Hashemi Rafsanjani, the former Iranian president who now heads Tehran’s expediency council, said yesterday that Iran had begun enriching uranium in 164 centrifuges.

This is no more than a pilot plant. Iran has stated it that hopes to run 50,000 centrifuges at its nuclear plant in Natanz. This year it announced plans to install the first 3,000.
Times Online