What fork is this?

[speedplay]

looks like an early ( very ) mag 20.
Seem to remember that the difference between the mag 20's I had and my mates mag 10's were that I had the dial and he just had a blank top cap with a needle valve in it.

 

[scant]

mag21s had a much more rounded style fork crown.

 

[cannondale king]

mag 20 i would say as well as thought