8 speed cassette on a 7 speed DA 7400 hub - possible?

I have a 7400 screw-on freewheel. 7 speed. Uniglide.

8-speed is possible, but you'd need a freewheel with the correct spacing. There's a model made in the far East currently but I'm not sure if it is the Shimano 4.8mm spacing.

The nice quality Sachs/SRAM model (OOP) is for Campag 5mm spacing.

Are 7 speeds not enough?

Uniglide ≠ screw on freewheel.

Uniglide is the last cog of the cassette being threaded and acting as the lockring.