Copypasta:
409 – Steel Steerer and solid crown, coil sprung, no external floodgate adjustment (Still adjustable with an allen key)
426 – Same as 409 with external floodgate adjustment
454 – Aluminium Steerer and hollow crown saving quite a bit of weight
Air U-Turn = Air Sprung with U-Turn function to allow travel adjustment
Coil U-Turn = Coil Sprung with U-Turn function to allow travel adjustment
Dual Air = Air Sprung with no travel adjustment (Saving weight by leaving out U-Turn gubbins inside)
The Air versions have been replaced by the Revelation forks for 09 so Pikes are a coil only fork now.
I’d be looking for 454 Air U-turn if you can find them, I like mine a lot…