1]Trepanning tools are used in manufacture of Gun Barrels, Pipes for oil well drilling, Large Motor and Alternator shafts and such parts.
2] They save time,electric power/energy and material as compared with solid drilling/ boring.
3] They leave a core which can be used for analysing and making other parts while drilling expensive materials.
4] Trepanning is the only process available to manufacturers where in large and long holes have to be drilled.
5] They can be used for drilling large holes in small length parts too.