How to rotate items and fix backpack placement
Quick answer
With mouse controls, pick up the item and right-click while holding it. Then check the highlighted cells before placing it: fitting the item and pointing its effect at the right target are separate jobs.
On this page
Rotate before rebuilding
Open the inventory, lift the piece you want to reposition, and right-click to turn it. Place it back only after checking its footprint. A player discussion documents this mouse action; controller inputs should be checked in the game's current bindings rather than inferred from the mouse button.
Check space and hands separately
A bigger backpack does not automatically let you hold more weapons. If the game reports insufficient hands, rotating the weapon will not solve that limit. Keep a working weapon equipped while you compare alternatives. Items such as Barbell and Robot Arm are discussed by players as ways to extend loadouts, but their current requirements should be read from their tooltips.
Keep the useful connection
After turning a support item, inspect which cells it marks. Make sure your intended weapon still receives the effect. Reorganize one piece at a time so a visually tidy layout does not silently lose the connection you needed.