What size box spanner would remove this backnut?

[adamt11]

I'd like to buy an individual box spanner rather than a set of them to remove this backnut from a small bathroom basin. What size box spanner would do the job?

Thanks

 

[Mottie]

Hard to judge but looking at other items to get a scale of things, I’d say 17mm. Won’t an ordinary 17mm spanner fit on it?

 

[sircerebus666]

https://www.wolseley.co.uk/product/rothenberger-spanner-set-for-monoblock-taps/

Sets are cheap

Like mottie says hard to tell from a picture

 

[Mottie]

Ah, I was looking at the wrong nuts! I think the one single brass nut is 11 or 12 mm. As S666 says, that set would be cheap enough to do what you want.