Having dipped out on a scrub today, I've been consoling
myself with some scrub-related net-surfing.
One of the great mysteries seems to be the radius of the blade.
So, maths and web time:
Obviously, we start we a NOS reference:
http://www.mjdtools.com/tools/list_071/20144.htm
(thank you Mr. Donnelly)

Now we need to calibrate: the page says the blade is 6 inches
long, and since we know the blade is for a #40 1/2,
(for cryin' out loud Jeff, it's a scrub plane, what were you
expecting?!)
http://www.supertool.com/StanleyBG/stan5.htm#num40.5
we know that the blade a 1 1/2 inches wide.

Pixel counting time.
left most pixel 14, rightmost 96, so 82 pixels are 1 1/2 inches, 54.6
pixels to the inch.
top pixel is 6, bottom is 334, so 328 pixels are 6 inches,  54.6 pixels
to the inch.
They match, which makes me happy.

corner of blade is 326 pixels, so the "curve" is 334 - 328 = 6 pixels
deep, which is
.11" (7/64")

The radius of this can be calculated:
http://www.egroups.com/message/oldtools/58360?source=1
r = h/2 + (l^2)/8h
r = .11 / 2 + (1.5^2)/(8 * .11)
r = .055 + 2.25/( .88)
r = 2.5"

So that's the radius Stanley ground a #40 1/2 scrub blade to.
Wether it's the best radius is another question

	BugBear