I believe he was referring to the buffer tube size.No idea what that means?
My lower is an Aero Precision and I'm thinking of getting the Luth-AR MBA-1 stock kit with their buffer/spring.
If you've got OEM Aero, you've got milspec; pretty sure you're fine on the dimension aspect.
However, the stock listed is for an A2 length tube. Your rifle may have a carbine tube; you'll need to check the length.