Hi guys sorry for the late reply just come on holiday for the weekend...... i dont think it matters what size the drill bit is i just took it to a friend of mine who got his biggest bit out and rammed it down.... even tried making the hole bigger by giving it a wiggle and trying from different angles so the holes are about as equal as a 20p and a 50p (figure of speech)...i was thinking about putting a hole in the bottom of the cans aswell the more holes the better the sound i would imagen.... i am also looking into getting some 2bros cans but for the time that i cant afford them i might aswell make good of what ive got