# Question about screw sizes

• posted on August 24, 2006, 10:26 pm
I noticed that as screw diameters become smaller, they convert to #'s. Would these be metric? For example you have fractional sizes, then 10, 8,6 etc.
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on August 24, 2006, 10:30 pm
No they're not metric.

<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on August 25, 2006, 1:00 am
snipped-for-privacy@hotmail.com wrote:

No they are not metric BUT....... the major diameter (od over the threads approx)
matches very closely to
.0625" + (screw size # ) multiplied by .0125"
check it out it helps me remember screw OD's
gets close enough
cheers Bob
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on August 25, 2006, 3:30 am
so since .0625 = 1/16 and .0125 = 1/80
a #10 screw would be
1/16 + (10*1/80) = 1/16+ 1/8 = 3/16? interesting.
thanks.
And when are we going metric?????
BobK207 wrote:

<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on August 25, 2006, 3:35 am
philkryder wrote:

Yup! I kinda geeked out one day.....I actually curve fit screw OD's in Excel to see if there was some sort of reasonable fit.....there is within a thou or two.

makes it easier to remember
cheers Bob
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on August 25, 2006, 4:12 am
So, you would use the same formula no matter what # the screw is? In the above formula, the only thing that changes is the screw #? BobK207 wrote:

<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on August 25, 2006, 4:57 pm
snipped-for-privacy@hotmail.com wrote:

the above formula, the only thing that changes is the screw #? <<<<
yes....just plug in the screw size number & you'll get the OD of the screw within a few thousandths of an inch.
so for a number 6 machine screw 6 * 1/80 + 1/16 = .1375"
# 6 screw OD is ~ .136" so the formula works close enough for me & it's easier to remember than all the screw sizes 1 thru 10
cheers Bob
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on August 25, 2006, 8:44 pm
BobK207 wrote:

I hold the screw next to the drill index and pick a bit that's smaller -- within a few thousandths of an inch, that is.
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on August 27, 2006, 2:52 am
HeyBub wrote:

I thought we were discussing screw OD vs screw size number
If you're trying to choose a pilot drill size.....just eye ball it.
Got bigger for hardwood, smaller for softwood
cheers Bob
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on August 25, 2006, 1:29 pm
philkryder wrote:

We're not.
In fact, since China makes most of our tools, we are slowly converting THEM to Imperial.
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on August 27, 2006, 8:46 pm
Ha! you think you can resist the logic & usefulness of the good ol' metric system?
Even England seems to be able to see the sense - well, sort of - (except on the road, a bit like they're a sort of a member of the EU).
BTW, Australia went metric in 1973, but you can still buy imperial screw sizes, in fact in woodworking & marine for example still use those wacky sizes....

<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on August 28, 2006, 12:58 am
Does anyone know "the history" of how these numbers came about?
For example, shotgun gauges are based on a pound of pure lead divide into equal sized spheres...
what are screw sizes and wire and metal gauges based on?
glenn P wrote:

<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on August 28, 2006, 3:59 pm
wrote:

Wire guage is based on how many holes in the draw-plate you pulled the wire through to get that size. I'm pretty sure that screw-sized are based on wire-guage.
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
• posted on August 29, 2006, 3:20 am

Nope, screw size numbers get bigger as the diameter increases. Wire size numbers get smaller. I imagine they do cross somewhere around #10.but not exactly.