These are height adjustable anti-vibration feet for Ikea Lack Tables. Each foot consists of two printed parts and a JB6368 anti-vibration pad that slips on the end. The female part is attached to the table leg and has internal threading. The male part has external threading, holds the anti-vibration pad, and screws into the female part which allows height adjustment to level the table. Amazon – JB6368 Anti-Vibration Pads

Source: Ikea Lack Table Adjustable Anti-Vibration Feet by RJFeddeler