High quality heavy-duty push-fit 4-01
It's for PTFE 2*4mm Tubing. For high grade all metal hot end or extrduer.
Bowden Connector that hold the tubing either broke or fell out is very important. This was likely due to the multiple jams and/or adjustments in the hot end that required removing the bowden tube multiple times. No biggy. Replace them with bit higher quality push fit you will have No problems any more.