The "nipple"
The "nipple" for refilling refillable canisters is 3D-printed with extremely small tolerances to ensure the tightest possible fit. Note that lighter gas is highly volatile, and some leakage may still occur during filling. I recommend refilling outdoors!
The "nipple" is mounted onto a lighter gas canister from Biltema. Apply a thin, even layer of contact adhesive to the metal pin and press on the nipple. If properly seated, the metal pin should now protrude to the same height as where the nipple ends.
The nipple also has a rubber gasket at the innermost end. Make sure it doesn’t come loose—if it does, you can reattach it with a small amount of contact adhesive.
Let the adhesive cure for some hours before using it, the pressure is high, so if you did not get adhesive around the metal pipe, it will leak