A key grip is actually the chief supervisor of a union crew responsible for moving lights, dolly tracks, cranes and scenery. While grips are primarily hired for their physical strength and construction skills, a key grip also has some administrative responsibilities.
This person works very closely with the head electrician, known in the movie business as a gaffer. As part of a pre-production movie crew, the key grip, gaffer, director of photography and a location producer will discuss the logistics of a specific filming site. All of these people must understand the needs of the script and have an understanding of how difficult a particular location shot might be.
The key grip must determine if lights can be rigged up safely on a mountainous set. It is the work of grips, working under the supervision of a key grip, to install these tracks and remove them after the shots.
Experienced grips with good work practices can be promoted to the position of ‘grip boss’. The grip boss works closely with the key grip in order to translate general orders into specific job assignments.
Most film work is contractual, so any qualified grip may be hired as a key grip for the duration of the production. Quite often the production company will hire an experienced and respected key grip and then allow him or her to handpick a crew. A film construction crew which works well together can help a director meet his own production schedule with minimal downtime.