Replaceable carbide blades

blades have four cutting faces.

five shank diameters

6mm 6.35mm 8mm 12mm and 12.7mm

two, three, four or six blades round the outside and

sometimes two flat blades on top ( listed as 2 + 2 for instance

these will potentially last a lifetime, the replacement blades are easily available and

cheap, 

these will not plunge,