What the Numbering on Phillips Head Screw Bits Mean
I mean — where does this convention come from?
Screws themselves have either a #numeric value or a fractional value. This refers to shaft of the screw. But what of the head and the tools used on them?
According to Fastener Engineer, Lee Dougan of the Phillips Screw Company:
. . . The original Phillips Screw driver bit goes back to the 1930’s. But prior to the invention of the Phillips® cruciform drive system, Robertson invented the Robertson® Square drive which was a marked improvement over the conventional slotted drive system that had been around for centuries. These drive systems were designated #0, #1, #2, and #3.
A #2 Phillips driver bit is approximately the same size that would fit into the equivalent screw head that would use a # 2 Square. Similarly, the #1 Phillips and #1 Square fit into similarly sized screw heads. So I think that is where the Phillips Screw designation came from. (It) takes you back to the Robertson square designation. A simple numbering system is an easy way to distinguish similar looking parts. It may be as simple as that . . . .
Note from the Host:
Please read below in the Comments section for the complete journey to our best answer above. I welcome continued discussion on this. A follow up post of sorts, here >> The Skinny on Screws :: A Guide to Common Screws.
Screws are one of the wonderous Six Simple Machines. More on all of them there. Thanks. ~jb @BuildingMoxie
6 thoughts on “What the Numbering on Phillips Head Screw Bits Mean”
To find this answer (that’s right, I didn’t know it) I set out on a 2-hour Google search marathon.
This is what I found:
1) Wikipedia ranks very near the top of most Google searches.
And there is some very interesting, though technical information, there.
“Drive Types screw bits come in many shapes and sizes.”
“(Phillips head screws) were originally designed for use with mechanical screwing machines.”
(Interesting tidbit on bolts — sidetracking:
The numbers stamped on the head of the bolt are referred to the grade of the bolt used in certain application with the strength of a bolt. High-strength steel bolts usually have a hexagonal head with an ISO strength rating (called property class) stamped on the head. And the absence of marking/number indicates a lower grade bolt with low strength. The property classes most often used are 5.8, 8.8, and 10.9. . . .”)
The Unified Thread Standard (UTS) is most commonly used in the United States of America, but is also extensively used in Canada and occasionally in other countries. The size of a UTS screw is described using the following format: X-Y, where X is the nominal size (the hole or slot size in standard manufacturing practise through which the shaft of the screw can easily be pushed) and Y is the threads per inch (TPI). For sizes 1/4 inch and larger the size is given as a fraction; for sizes less than this an integer is used, ranging from 0 to 16. For most size screws there are multiple TPI available, with the most common being designated a Unified Coarse Thread (UNC or UN) and Unified Fine Thread (UNF or UF).)
2) There is an association dedicated to American Fastener History:
3) There are a handful of good articles out there on how to use a screwdriver properly:
“To safely use a screwdriver, first select the appropriate tip and size to fit the fastener’s head.”
4) There are certainly some interesting and worthwhile web ventures that have been abandoned:
5) diy.com usually has good info:
“(Phillips bit) sizes can range from 0 to 4, with 0 being the smallest.”
Fantastic chart at the bottom of this page!
*That said it appears that the answer to my question lies somewhere, I think, within the annals of ANSI http://www.ansi.org. And while I couldn’t find it today, maybe I pick this up another day.
Feel free to provide further insights, and help me answer this question below.
On a whim I emailed Mike McGuire the publisher at the American Fastener Journal.
He got back here was his reply: “I would go directly to Phillips Screw, but the #numbering system has to do with the size of the Phillips recess. #2 being the most common and widely used in commercial fastening. #1 is used in small diameter (miniature screws) Seldom have I ever seen a #3 or #4.”
While I will try to track down the Phillips screw company — visit Mike and the Journal @ http://fastenerjournal.com/afj/ for eZines, videos and links to http://usfastenersources.com.
This morning — I shot off an email to Phillips Screw (http://www.phillipsscrew.com). Yes, The Phillips Screw.
[Moved to body of article]
I am not saying that I have looked much over the last few days – but it seems that an answer as straight forward as this is not easy to come by . . . and I’ll roll with it.
Thanks Lee, and thanks to Phillips Screw for getting back so promptly.
#3 Phillips screws are used in coated decking screws and can also be removed by a #2 square head, as their base is mostly square. So you have two options with which to drive them. I personally like the square head better…
I’ve been somewhat surprised by how many people are searching “What is the most common phillips head size?” The simplest answer is #2 — as this serves drywall screws (great self-tapping general purpose screws) and wood and metal screws up to #9. #3 is important too for screws sizes above #10 and for some exterior deck screws — (great general purpose screws when moisture is a factor). The best exterior screw is stainless and these are usually found with a square drive.