I reuse my old Bic flints. Larger in diameter than many and work great in a Dupont, can't speak for a Dunhill though. I use them in Dupont and several other brands. You have to use a pair of side cutters to cut them to length as when you tear the old Bic apart and recover the flint it is still over a half inch long. Be careful when you're tearing the old Bic apart because there is a spring under the flint and if not careful it will shoot across the room, or in you eye

I reuse them all the time. I just use a pair of needle nose, firmly grip the flame shield, grab it with your hand covering the spark wheel so it the flint doesn't shoot out and give it a twist. After you remove the flame shield the spark wheel may still be intact so youll have to grab that and give it a twist, again,make sure your hand is covering it or it will shoot across the room. No need to be gentle, you're just trashing everything but the flint. Any flint should work just fine as long as it fits. Some are different diameters but if it fits in the lighter it should work. Don't force a over sized flint or you'll end up with problems.