Every aircraft needs dozens of holes to be made that range from about 1/4" to a full inch in size for mounting things like headphone jacks, toggle switches, circuit breakers, ignition switches, charging outlets and much more. Many of these holes need to be made in sheet metal or other thin materials. Trying to maintain a collection of large diameter conventional drill bits for these jobs would be impractical and expensive. The step drill (aka Unibit) is a fantastic, affordable solution.
Many holes that are created by step drills are also used to pass wires and fuel lines through wing ribs and bulkheads within the aircraft. Abrasion from the sharp edges of these holes needs to be eliminated by the use of grommets and bushings placed in these holes. For very large or irregular-sized holes we need to make use of flexible grommets. The video in this week's Tip demonstrates the choices available to builders.