Bushings are nominal bore diameter for specific caliber. Bushings fit removable pilot tooling.
Drill bits are standard "jobber" length. Bit and bushing is used to drill the rifling out of a barrel to install a sleeve inside the barrel (replacing the rifling).
Material: Tool Steel
Drill bit extensions will be necessary for other than short handgun barrels and extensions are usually made by welding steel rod to the end of the drill bit.
Pilot drill bit bushings are for use with ECT drill bits only.