How does one attach a sling to an AR15 with this style of stock?
With one of these:
https://www.amazon.com/Magpul-QD-Quick-Disconnect-Sling-Swivel/dp/B00HKBSQ26
How does that fit though that hole?
Something like that is needed, but there's more to it than just that part.
The tang with the retracting balls goes into the hole and locks in place. It doesn't go all the way through.
A small loop of para cord will work in a pinch.
On a related note, sometimes attaching slings to the sides of stocks can have an effect on the directional pull of the sling. Not always a bad thing, but sometimes it can be less than ideal.
I've used a zip tie, making the loop large enough to attach a J-hook.
Looks to me the hole might be too small for a QD? A loop of paracord and a magpul paraclip is my solution:
(https://i.imgur.com/zak3PLl.png)
I think that those are two different stocks.
Aviator1968, could you share the make and model of the stock? Or a photo of the whole stock?
Three slightly different models, all needing a similar attachment method.
I would just use a loop of cord or a doubled up pair of heavy duty zip ties. (doubled because I never trust the locks on zip ties)
This works fantastic;
https://grovtec.com/products/buttstock-sling-tail-gtsl117
That is not a Quick Detach port, so the QD swivels alone would not work. That may be a place that a QD port could be installed though. If you want to go that way, search for parts specific to the brand of stock. I think your best option is the paracord like you already did.