A fork is what holds your front wheel, and it fits into the scooter deck to connect to the handlebars.
There are a few critical things to consider with a fork. These are - wheel size compatibility, Fork size (as this effects which compression system to use), and handle bars compatibility.
Wheel size is the most simple, just make sure the wheel that is wanted to be used will fit into the fork and Spin.
Fork Size is the next topic – there is a ‘standard fork’ or an IHC fork. The Standard fork will work with SCS and HIC compression systems, and in some cases ICS compression. An IHC fork is a narrow gauge fork that only works with IHC compression. ** some conversions are possible as well. Its best to read more about this in the section Scooter Compression and Clamps
Handle bar selection is really dependant on the compression system being used, but it is dictated by the fork as well, so Forks, Compression and handlebars really need to considered as a group.
Forks are generally forged or machined out of high grade aluminium and are heat treated. Apart from the functionality aspects to consider, it then is really about colour and style and brand reputation.