Marv, and inquiring Galoots

I just went down to the shop and opened a clearly-labeled original box of
McFeely’s flathead square drive screws. I hold one in my hand as I tap out this
message!

The McFeely’s square drive recess IS NOT the same as shown in that Robertson
patent.

There’s no chamfer angle at the mouth.  

The bottom of the recess is not a neat pyramidal shape as shown in the patent.
Rather, it looks hemispherical
 in nature.

The recess itself has “vertical” walls.

I think the Robertson is the better design in terms of getting the driver
quickly seated into the hole.

John Ruth