Advice for looking at used semi-mounts

[Amistica]

I am looking at semi-mounts on loupe troupe and diamond bistro, and my question to you all is this: How can you know if your stone will fit? Is there a certain size tolerance? My stone is a 7.5 x 7.5 cushion spinel (I don't know the depth, looks to be about 6 mm). Would this fit in a setting that previously held a 6.92x6.42mm cushion? If anyone could let me know what tends to be the norm for size adjustments when trying to place your own stone into someone else's (and in this case, custom made for the stone) semi-mount, it would be much appreciated. Thank you!

 

[distracts]

I try to be within 0.2mm of the previous stone. For fancy shapes, I also like ALL the measurements, not just LxW but also the diagonal measurements.

For that particular stone and that particular mount, I don't think it would fit.

 

[Amistica]

Okay, that is good to know. 0.2 mm doesn't give a lot of wiggle room, so it has to be an almost dead-on match then. Moving on in my search, then. Thank you!