This is a handy tool that helps you join filaments 1.75 mm diameter. I have tested it with PLA You need a soldering iron with variable temperature. I have used 180 degrees Celsius for all of my joins. Only this tool worked for me and gave me repetitive results Made with FreeCAD Do not use lighter or a soldering iron without temperature control it will just burn your PLA. Set up : Step 1 ) Print the item using 20% infill 0.2mm or more layer height Step 2 ) Infill a PTFE tube at the 4mm hole and cut the tube flush Step 3 ) If you need to extract the joined filament not from the end of it cut the PTFE tube like the picture Step 4) Insert the two M3 nuts Step 5) Screw the two M3 8 mm bolts How to use : Step 1 ) Insert the up (old) filament from the top that has the PTFE tube (blue filament at the pictures). The top filament should be 2 mm out from the PTFE tube Step 2) Use a screw driver in order to adjust the top screw in order to increase friction at the top filament but at the same time can slide Step 3) Infill the (new) filament from the bottom (black) Place it 5 mm from the bottom. Step 4) Secure the bottom screw firmly. Step 5) Use the soldering iron at 180 degrees and heat both of the edges at the same time Notice that the edges should not be placed at the center of the pliers. The top edge should be shorter that the bottom one. Step 6) Squeeze the pliers