hey Kevin, I'm not sure if you got my last post so I'm sending it again. The hole on top was about 10 mm in diameter and the piece from lezyne was about 12 in diameter so I found a drill bit that was a little under 1/2 inch and it was perfect so I guess I took out about 2 mm. The bottom hole was a bit small also but I just left it. Maybe our lights have different size pieces. Mine is the mega drive I think. Anyways, I hope this helps. I'll attach a link to a Dropbox file with the pictures in it.