I have just examined my 4350 Jigsaw.
The slot that accepts the blade is always set fore & aft - it does not rotate.
A Locking collar rotates against a strong spring and exposes the full slot - when the spring's released the collar closes on the blade.
You can see it in action here...
https://www.youtube.com/watch?v=SBrXq_BcDLs
Good Luck..., March 2016