Purdy 9" roller/ cover confused

[GRUNT16V]

Hi
I have just purchased a purdy 9" roller but I'm confused about what roller head to use I'm painting new plaster i have already sealed with a wash coat
Any recommendations i was thinking colossus heads but have just noticed its for rough to extra rough but I don't want a skinny head as they leave tramlines etc any help would be greatly received
Cheers

 

[joe-90]

Go for a medium and thin your paint or you'll get roller stipple.

 

[GRUNT16V]

Medium yes but what do purdy call it ???? Colossus , white dove etc cheers