Well I can't specifically tell you what size bulbs are behind the buttons themselves but last time I checked on my 6th gen, I think they were 3mm bulbs, but don't quote me on that. the lights above I know for sure are 5mm and the clock is also 3mm, but for that you WILL need a resistor. I can tell you the size that you need for that if you go to the site that I have. You can use the surface mount or jst the other type of resistor, but it's recmmended to use the surface mount since it will be less of a hassle to reinstall. I haven't had any luck with finding surface mount resistors at radio shack, so you might want to check online or other electronics shop.