Possible Clues:

• It can be boring
• Army work for leaders of basic infantry training - that's bound to be boring!
• Sharp and penetrating thing, part of exercise?
• Chuck insert
• Removable cutting head in a boring instrument
• Revolutionary Head's training was effective
• Large monkey used teeth to go round and in
• Part of routine that can be a bore?
• Cutting head
• Exercise: a modicum that bores