In mechanical action, the keys are directly in front of the pipes and wind chest so the connection between the key and valve follows straight lines and right angles. Sometimes the architecture and space available necessitate the placing of the pipes off to the side. Then the connection must follow straight lines at irregular angles. The roller, a wooden rod, is used in this circumstance as its rotation can accommodate the irregular angles. It has two arms at each end. One is attached to the key (or pedal) and the other is attached to the valve directly, or trackers which lead to the valve. The roller mechanism is frequently used in the pedal division and is only found in mechanical action instruments.