What is the maximum size of the SSD?

Hi,

I'm willing to upgrade my Mid 2011 iMac, putting in an SSD disk and creating a fusion drive.

There are several SSD's on the market, but some of them are a little bit thicker than others. I'm having an offer for an SSD with a thickness of 9.5mm. Will this fit in my Mid 2011 21.5" iMac, or should I order a thinner one?

In the online guide, no measurements about a maximum size is mentionned, but I would lik to be sure that I will be able to close up my iMac again.

Any help is appreciated!