Question about screw sizes

[shareyourknowledge]

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.

[RBM]

[BobK207]

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

[philkryder]

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:

[BobK207]

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.

your explanation ......

makes it easier to remember

cheers Bob

[shareyourknowledge]

[HeyBub]

We're not.

In fact, since China makes most of our tools, we are slowly converting THEM to Imperial.

[BobK207]

the above formula, the only thing that changes is the screw #?

[HeyBub]

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.

[BobK207]

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

[glenn P]

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....

[philkryder]

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 > Ha! you think you can resist the logic & usefulness of the good ol' metric > system?

[Goedjn]

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.

[gfretwell]

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.