Unfortunately,

> Phillips heads, apparently to get around patent issues, come in all

> sorts of sizes, tapers and nose depths.

Ummm, no they don't. The term "Phillips" only refers to ONE type of crosspoint screw/driver. There are only a few more sizes than Robertson:

#00, #0, #1, #2, #3, and #4

Now, there ARE other types of cross-point fastener head. And this is where you get into different tapers and nose depths.

In the early 50's, the Posidriv screw head was manufactured by the Phillips Screw company. Here is an article about Posidriv screws. They allow for more torque to be used before the tool slips out of the fastener.

Yet *another* cross-point screwdriver is the Reed & Prince. Why? dunno.

Here is more info:

===

There are 3 different screws and screw drivers that all look somewhat the same but are not interchangeable.

1. Phillips (most common of cross point style screws)

A. Straight side ramps, rounded nose.

2. Reed & Prince (used mainly in aircraft and marine apps.)

A. Straight side ramps with sharp pointed nose, steep ramp angle.

3. Posi-Driv (used in GM vehicles since early 80s)

A. Curved side ramps, extra flute between ramps and curved nose.

===

So THERE! There is only ONE Phillips screw!