These are adapters which allow you to attach World of Nintendo 2" Metroids to the average 3mm poseable figure stand like Tamashii Stage Act, Gundam Action Bases, or the default Figma stand.
The hole is 3mm and the peg is 2mm. Can theoretically be used for other toys that use 2mm holes.
A single adapter can be found here:
https://www.shapeways.com/product/UABKB4PPQ/3mm-to-2mm-adapter-for-2-quot-won-metroid
A set of three adapters can be found here:
https://www.shapeways.com/product/5EXU8YL6M/three-3mm-to-2mm-adapters-for-2-quot-won-metroid