Originally Posted by Pawel.W
it is the mortise and tenon neck joint.
When i put in the neck in the mortise there is about 0,7 mm gap on the sides.
make shims that keep the FB properly centerd. There will be no noticible tonal loss as long as the shims are good fit. I like to make and dry fit proof my shims then glue then first to the tenon. Effectively making the tenon wider. That way you glue in the neck as if it normally would. this is a common and simple fix to do.
It will take some dry fitting and measuring to be sure you keep your neck alighnment in relationship to the bridge correct.