A tool which enlarges a bore during a pull-back operation by compression of the surrounding ground rather than by excavation. Sometimes used during a thrust boring process as well as during directional drilling/guided boring pull-back.
A MIDI expander is an instrument that has no keyboard and can only be played via its MIDI IN socket and an external keyboard or other controller. Sounds are sometimes preset and non-adjustable, but some of the more recent units are quite versatile. Originally intended as add-ons for organs, the better expanders potentially have much wider application.
A plug that is slightly wider at one end to be used to stretch or enlarge a piercing.