One is C. Krebs' Patent issued on
May 12, 1868 and assigned Patent Number 77,819. It's cutting
head consists of two wings rolled into a conical configuration
with the margins of the wings sharpened.
The first photo shows two such
countersinks on the left and a preform on the right that exhibit
the shape of the wings before they were rolled into a cone. The
preform is illustrated on the patent drawing and 35 years ago I
found one that had escaped the rolling process in the factory.
The last photos exhibit a large handforged specimen that has a
2-inch cutting head.
The two specimens on the left are Kreb's
Patent of 1868.
The specimen on the right is a preform for this countersink
the head was rolled into a cone configuration.
This is a close up of the cutting heads and
This is a view of the cutting head looking
into the top of the cone.
This photo illustrates a very large handforged
countersink that has
a cutting head 2 inches in diameter at the top of the cone.