We purchased these with the 20cm expanding feet for our trumpet section to get a level above our trombones. It is true there are no instructions regarding attachment but after a few minutes it was quite obvious that the expanding risers have a little lip which slot under the corresponding gap on the underside of the platform. Once fully expanded and "locked" into the square space at the bottom, the platforms are super solid. They have the perfect balance of being solidly built, sturdy, and yet light enough to easily transport. Would definitely buy more if I had the need. Again, Thomann delivery and dispatch was top notch.