The following is my experience as I learned the process for attaching the wing (root) to the fuselage. Both main and rear spars come predrilled with 3/16” holes at the root attach point. The fuselage attachment fittings are predrilled with 1/4” holes. The end result is to attach the wing root to the fuselage by match drilling the main spar to the front attachment fitting to 3/8” (AN-6), and the rear spar to the rear attachment fitting to 5/16” (AN-5), both left and right. So we are enlarging existing smaller holes in both the spars and the fuselage to match the aforementioned sizes.
But first, wings on all airplanes have a set Angle of Incidence. And the Angle of Incidence for both wings must match each other when installed to the fuselage. The Bearhawk factory does amazing work building their fuselages and wings. Their pre-established attachment points are extremely accurate. However, the wings Angle of Incidence is a fixed design feature that MUST be checked by the builder and can require some fine tuning.
What is the Angle of Incidence? On fixed-wing aircraft, the angle of incidence (sometimes referred to as the mounting angle) is the angle between the chord line of the wing where the wing is mounted to the fuselage, and a reference axis along the fuselage (often the direction of minimum drag, or where applicable, the longitudinal axis). The angle of incidence is fixed in the design of the aircraft, and with rare exceptions, cannot be varied in flight.