Needed an adapter to connect micro to classic size pieces. I found the model set of parts and pieces Yuri and I took the smallest single connector from both sets micro and classic and trimmed the hole off each end and connected them to look similar to the original k'nex part using Tinkercad.  I printed with a .4mm nozzle set with .6mm line width so its all wall and some are single. may need to adjust to your liking. photo is of original part from the K'nex kit.