This is a three part weight holder for spools. It is intended to be used in the BambuLab AMS. When the spools get low on filament they sometimes lift up when filament is being pulled from them. With this inserted it helps the spools roll as intended. A bit of glue on the inner threads for the top part of the weight holder will keep the top on when the cap is unscrewed. The weight I used is this one: https://www.amazon.com/gp/product/B08GC3958M/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1