What the Numbering on Phillips Head Screw Bits Mean
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Question:
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?
Answer:
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 . . . .
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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
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.
http://en.wikipedia.org/wiki/Screwdriver
“Drive Types screw bits come in many shapes and sizes.”
http://en.wikipedia.org/wiki/Screw
“(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. . . .”)
http://en.wikipedia.org/wiki/Screw_thread#History_of_standardization
http://en.wikipedia.org/wiki/Unified_Thread_Standard
(More sidetracking:
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:
http://fastenerjournal.com/afj/
3) There are a handful of good articles out there on how to use a screwdriver properly:
http://www.acehardware.com/info/index.jsp?categoryId=1266832
http://www.thisoldhouse.com/toh/asktoh/question/0,,20058438,00.html
http://home.howstuffworks.com/screwdriver.htm
“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:
http://www.sizes.com/tools/screw_drive.htm
http://www.sizes.com/tools/wood_screwtbl.htm
5) diy.com usually has good info:
http://www.doityourself.com/stry/typesofscrewdrivers
“(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.
Thanks Mike.
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…
Thanks Holly!
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.