The underside of the top cap of
the Feather AS-D2 razor has a square “post” at each of its four corners that
corresponds to a matching cutout at each of the four corners of a standard DE
blade; the top cap’s posts mate snugly into depressions or “sockets” at the
corners of the standard AS-D2 baseplate, allowing the top cap and baseplate
together to clamp the blade very firmly on both sides along the full length of
the blade near to the cutting edge; this is an unusual design feature of the
AS-D2, and, not incidentally, it ensures that the blade will be perfectly
aligned between the top cap and baseplate when the pieces of the razor are
tightened.