Reach check: the joint between your pipe and the head
Say which piece you are replacing, where the water leaves the wall and what has to change, and the list drops to parts that fit that run.
Pick an answer and the list narrows.
Shower arms bring overhead clearance out from a wall or down from a ceiling, while flexible hoses connect water supply elbows to handheld sprayers in a bathroom or RV. Slide bars mount directly to tile or wall panels with screws, holding sprayers at adjustable heights. Selection begins by identifying whether the replacement involves extending a fixed shower arm, adding a flexible hose run, mounting a slide bar, or changing an adapter or flange.
Outer pipe diameter and thread standard dictate what connects at the wall. Measuring across the external threads of an existing shower pipe or arm outlet gives the exact size, typically standard 1/2 inch IPS or G 1/2. For slide bar replacements, measuring the center-to-center screw spacing between existing wall holes determines the required bracket span, while slide bar holder clamps require measuring the outer tube diameter of the bar itself.