Super slim roller to fit behind radiator?

[OpenToSuggestions]

Hey all.
I am in a fairly new build house and upon decorating it is a pain in the rear painting behind radiators due to space. A regular 4" roller would get paint on the radiator.
My Dad has a long reach roller arm with a super slim roller on it that he has for many years. It is probably only 15-20mm diameter. I am free to borrow it but it is far easier if I buy my own!

Does anyone have idea what these are called? I am struggling to find one online.

Could it be termed a mini roller? I am not fussed about having long reach, just a small diameter roller!

https://www.amazon.co.uk/PRODEC-100mm-GLOSS-ROLLER-PRRF002/dp/B005FF5KTG/ref=asc_df_B005FF5KTG/?tag=&linkCode=df0&hvadid=399647016194&hvpos=&hvnetw=g&hvrand=2796072490261249025&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1006674&hvtargid=pla-853954996541&th=1&ref=&adgrpid=85427416059

 

[OpenToSuggestions]

Thanks for the replies.
I've had a look at all of those but they don't appear to be as thin as the one I have used.
There is the option to unhook the radiator if I am totally stuck as it does have the plastic flexi pipes .