A non-countersunk screw head is if the head from the screw is completely exposed outdoors your workpiece/materials. You should use a flat head screwdriver to insert or eliminate screws that have a linear notch during the screw head. JIS screwdrivers are available in many measurements and types, such as flathead, https://typesofshingle59258.onesmablog.com/the-single-best-strategy-to-use-for-types-of-screw-heads-list-69693817