Nut centering tool for welding

[Toolmaker51]

Flathead/ Countersunk screws have potential for centering, if the receiving hole has equal angle (ie deburring). Some try to use countersunk holes as locators (like dowels) with misconception the angle performs to draw an item this way and that. Unlike Tuomas's screw which was machined (if in one chucking) will be concentric. Flat head screws despite looking the same are not, therefore rarely share a common axis.
It's easy to prove. Fabricate a plate with 3 countersunk holes inline or triangular pattern, matching 3 flat head screws, even sockets, which are closest.
Run the screws in and number them with felt tip. Locate the position accurately, via dial indicator, height gauge, depth mic whatever you have. Remove the screws and place in different positions than previously and re-measure. Another demonstration is multiple screws tried in a single hole, Clamp plate vertically, touch with an indicator and turn in a succession of screws; the plate will rise and fall as countersink contacts underside of head.
Part of reason aircraft screws are 100° not 82° reduces head height, = thinner material, hence lesser weight. Another is that concentricity problem, raising a point of stress in said panel, that the increased angle and shallower hole moderate.

For most things, the flathead screw will perform as you wish. Just be aware, assembly time, some tuning might be in order.