These allow for a simple and low cost method of locating the holes for dowells. Simply drill the hole in the first piece (accurate centering is not essential) , insert the dowell pin and bring the mating piece together and tap it which l
These screws need a jeweler's screwdriver or similar - round Phillips head. Metric dimensions are nominal and specified as Overall Length x Shank Diameter Under Head x Head Diameter. See below for size and gauge code.