Looks like the thunderhorn has the same gripper as the selway so you could buy the small gripper from selway and use skinny arrows. They just slide into the metal rail.

I wondered about swapping with Selway. I never had both at the same time to try that. I figured if you could Thunderhorn would have offered the option in the first place?

I think selway now has one with small grippers inside larger grippers all in one.

I would like to complicate your decision even more 
https://marksmanquivers.com/a/review/all
Scroll down for some reviews to see what people think.

Regards
Mark

I use Selway side mount if the bow Has inserts as my preferred option.  I have a Thunderhorn strap on on one bow and had to get a Selway gripper for it to hold my carbon arrows tight.  Other wise they both work.  If buying a strap on I would get the one that looks best on my bow.

I love the Thunderhorns & have 6 or 7 of them, all 3 kinds. An earlier post stated that they don't offer grippers for smaller diameter arrows, but they do, and they work fine-I use 'em for one of my bows that shoots Centershot arrows. See the link below:

https://thunderhornmfg.com/collections/accessories/products/snuggers

I have had Selways but have since switched all quivers to Thunderhorn.