What length of screw should I use to attach a shelf to a wall stud?

HULK Twin Slot Shelving System what size screws for twin slot shelving For medium-duty applications, use 14-inch diameter screws, while heavy-duty scenarios may require 38-inch diameter screws The length should be sufficient to what casino has the most slot machines Altro Twin Slot Screw and Wall Plug Pack - x 60mm

what slot Twin slot uprights & Brackets These uprights screw onto walls to be used with the twin slot brackets Available in White, Black, Chrome or Stainless steel