@somethingnicer Best to leave a lttle bit extra on the flat area for the nut. When you sand it to take the router marks off and leave a nice smooth finish, that will reduce the flat area a bit. So…   Read more»

@somethingnicer 
I’m thinking that the wooden filler strip has been taped on to the trussrod to protect it during transport.

 This is what my trussrods look like. A round steel rod and a flat steel strip.

Thats a good comprehensive answer you’ve had from Brian. I’m a wee bit confused with your wooden truss rod, can you post a photo of that.