there are three drilling steps for the hardware in the upper tenon: first a shallow flat bottom hole is drilled for the top of the t-nut, then the neck is attached to the body and bolt holes are drilled through the top of the tenon and head block, then the neck is removed and the bolt holes are widened in the tenon to receive the threaded part of the t-nuts. i was careful to support the edges of the tenon and to put a sacrificial backing where the bits break through.