Most keys will fit without any issue, as long as the hole on your key is greater than 4mm in diameter, it has a flat profile and the length is shorter than 67mm (from the hole to the end of the key). This rule also applies to keys where the holes are irregular in shape (e.g. slot, square, triangular).
Anything that doesn't fit on the Orbitkey (such as car keys) can be attached using the D-ring included with every Orbitkey.
If you want to make sure, we have a guide to how you can check your keys in the next question.
In regard to longer keys, the Key Organiser can accommodate keys that are up to 67mm long (from keyhole to the end of the key). For your longest key, we'd recommend to place it in the middle of the stack for a better fit.