As stated, hub-centric, which is something that is easily overlooked. Hub-centric means that the hub locates the spacer rather than the wheel bolts.
Keep in mind that regardless of whether a car uses bolts or studs, the force that is keeping the wheel on the hub is friction between the two surfaces, which is attained by the bolts through their recommended tightening torque. Lugs are never under shear; if they were, you'd shear them just letting the car off the jack, provided the wheel had no other means of location.
As long as you can maintain the correct tightening torque, and thus force of friction, the wheel is properly fastened. Keep all surfaces free of any lubricants.
But all this is irrelevant as wheel spacers suck. Bearings don't like additional axial leverage.