I have this threaded fork that only reaches the top of the head tube.
I can fit the first part of the headset (see photo) but no other nuts (?).
Can I use it like this ?
Can I use it like this?
Yes, you can use it like this.
But, if you do the top adjustable cup will loosen as you ride causing:
Don't ask me how I know :)
A fork with the correct length steerer tube is the best option. You need a different fork.