Router bit holder for ½", ¼", 3/8", 8mm bits. The ¼" version is available in a 6x6 or 3x6 configuration. The other sizes in 5x5 or 3x5. Doesn't need to be super strong so PLA and low infill are fine. This is a redesign in OnShape of something I did in TinkerCad. The pattern tool makes designs like this easy to modify.