Shock absorber tool : which size?

I did a research and could not find the exact answer other than what Doug called “shock absorber socket”.
I have to admit I did not know that a dedicated tool existed.

The front shock absorbers isolators need replacement. Lock bolt is almost impossible to remove. Like many others before me, I tried vice grip and then impact gun. Nothing worked.

So now I’m educated (thanks @Doug_Dwyer ) I’m trying to find the right size for this tool.
Local shop has a wrench, 5x8mm and 6x9mm.
Will it do the job?

Thank you for your help!

I think it may help other members, so here is a little update.
Yesterday, I went to garage and checked the shocks in-situ :shock head seems to be 6x9mm.
Not 100% sure, because someone tried to tackle this job before me and metal is a little messed up.
I’ll let you know as soon as I get the tool.

I’ve always got away with a small adjustable spanner onto the square head of the shocky shaft. However if priors have mashed it try using a small file and try and get back the square head of the shaft. Some WD40 on the offending nut might help.