Small buttons placed in a row between the manuals. When pressed by the organist, the piston (which is effectively an electric switch) sends an electrical signal to the combination action instructing it to put on / take off those stops set for that piston. Conventionally, the pistons operate the stops of the manual above them (see also ‘Generals’).
![](https://toff.org.uk/wp-content/uploads/2015/11/Piston-1024x768.jpg)
Sometimes referred to as ‘Thumb Pistons’ to differentiate them from Toe Pistons.
Thumb Pistons may have a second touch, most frequently used to bring on pedal combinations.