Tamiya calls for a 3.5mm hole drilled into the bottom side of the wing halves. They actually give you a nice guide for the drill bit molded onto the inside. I didn't happen to have a bit of the correct size so I improvised with a 3.5mm cannulated reamer and K-wire used in orthopedic surgery. First, the K-wire is used to drill out the guide hole. The cannulated reamer is slipped over the wire and the hole is reamed out. The cutting end is very precise so it leaves a perfect hole.