Rail system question

Bobalos

Private
Minuteman
Nov 1, 2023
32
15
San Diego
I'm looking at an adm base for a bi-pod and their website says "....to accommodate both in spec and out of spec rail systems. " What does this mean?

The answer to the above question might answer the next question.... but here goes. Does this fit a picatinny rail or will it fit an arca rail? (Or neither).

Thanks folks
Bob