Spanner for Stern lock?

[Mfresh]

The key has snapped off inside my GB coin door lock, but luckily the door is open, so I just need to change the lock, and I have plenty of spare ones.

But I cant seem to undo the ring on the inside of the door which fastens the lock to the door. Anyone know what size spanner is needed for that ring? I've tried a metric 21 which is too small, so it will be an imperial spanner a bit bigger than a metric 21mm.

I'll to buy one as my imperial spanner set doesnt go big enough, so I need to know exactly the right one to buy if possible.

Thanks!

 

[J.C.Rox]

I just pulled it tight with a set of grips when I changed a lock previously and that did the trick..

 

[JT.]

Probably 7/8th. But personally I'd just buy an adjustable spanner, 'cos they are useful for other jobs too: https://www.amazon.co.uk/Stanley-09...1492337867&sr=1-4&keywords=adjustable+spanner

 

[Mfresh]

Thanks for the advices. I got it off in the end with an adjustable spanner, but it's got to be easier with the right size box spanner! Took about half an hour...

Cheers,

Paul