This is a part of the Bicep. I use PLA, and it's not as soft as ABS. So when I tried to mount them together, it was impossible, because it wouldn't flex. But PLA gets soft at relativley low temperatures, so I used a heatgun at a low setting to heat the connections. After heating the plastics for a short while, it was easy to mount them together. I think it's possible to use a hairdryer too, but I never tested.