This is a thrust bearing holder I made to improve the quality of my MendelMax 2 parts. I think the lack of a bearing to hold the Z screws in place at the bottom. It seemed like hanging the Z screws by the helical couplers wasn't helping, so I put them in a very slight compression with the help of this part.This part requires two 688 bearings.An isolator is required for this part to work well. I recommend this one: https://www.youmagine.com/designs/jd-mm2-mendelmax-2-z-isolatorsThis seems to improve part quality a lot.