The steering column lock in my Bella had been (quite forcefully) removed at some point in the past.
Unfortunately I sent the frame for powder coating before repairing the lock holder; I needed to bend them back into shape after the paint job. Luckily without damage, but not ideal.
This is what the lock holder looks like:
As you can see, the end of the metal flares outward as a result of removing the lock in the past.
I managed to find a new old stock lock on the internet for the Bella; Anna Giordano from myoldscooter had one on offer:
Missing are the spring at the front and the retaining clip. Those I ordered from Helmut and Iris Bougé. The spring I do not have a photo of, but fits tightly around the front and make the front total diameter equal to that at the start of the lock.
The lock itself is very simple. In the unlocked position the small pin halfway down the lock is in the groove in the lock. I the locked position it fits in a groove in the frame. To lock it, move the key to the unlocked position, push the entire lock deeper into the frame and move the key to the lock position. The pin will then fit into the second groove in the lock holder in the frame. You can see how this works in this picture:
You can also take the entire lock out using this procedure if the retaining clip is removed.
The clip can be seen at the end of the lock holder:
Finally, the hole at the bottom of the lock holder can be used to hold a grounding wire.