I use 3 sodastream gas cylinders, and walk to the shop to exchange them. Usually I exchange only two, but once in a while all 3 are empty, and it's clumsy to carry them.

So I designed this handle to carry from one to 3 cylinders (the recent ones called “Quick Connect CO2 Cylinder” with a pink label and without a screw neck).

This design uses 2 cool things:

• Optional: two embedded magnets: you need to pause the print of both halves to insert the magnet in place before resuming (see pictures). The provided gcode has this pause included.
• One "print in place" hinge. It has a 0.15 clearance between moving parts. It needs to be printed standing, not flat.

If you don't want to use a magnet, or if you find the magnet link too weak (honestly it's a bit weak unfortunately), you can print the two parts of the “lock” and use four philips screws (M2x12 to M2x20) or glue. It will be a bit difficult to operate the few first time and then gets easier.

The hinge could probably be glued too, but I've used four hex screws and nuts:
Two M4x12 and two M4x20. The nuts go into the slots designed for them.

The magnets are 20x10x2mm

I've printed the whole thing without support.

Layer 0.2 for the handle halves, 0.15 for the lock and the hinge.

Infill 20% for the handle halves (increased to 35% near the hinge) , 35% for the hinge itself, 45% for the lock.

I've increased the infill near the hinge so that the screws have a stronger hold.