This is a Model M400 Adjustable Helicoid Spiral Staircase designed by Roger Tallon in 1964. It is currently in the design collection of MOMA.

Tallon was one of the leading figures of French industrialization. He studied engineering in Paris and later taught at the École Nationale Supérieure des Arts Décoratifs where he co-founded the Department of Design. Tallon is mostly known for his work with the French National Railway. He worked on TGV bullet trains, designing carriage interiors, brand identity and everything in between. He later became Design Director of the Eurostar.

The stair has a central steel pole on which cast aluminium steps are stacked and attached with two screws. Three different widths of the stair were designed, ranging from 550mm to 900mm. There is also a wide landing stair. All steps have of a rubber inlay. 

The assembly also includes spacers and baseplates but no handrail, opening up opportunities for bespoke solutions.

The stair is 1400mm in diameter and can extend up to 4m in height.

The M400 is still in production. In 1986 Sentou acquired exclusive distribution rights and are selling it for €10,000. You can also get used individual steps in auctions for €500 a pop.