Screw Size for Dummies

Assorted screw types

When you come right down to it, some of the rubbish that makes it onto the internet is downright hilarious... or it would be hilarious if it weren't outright ridiculous. While we're fully supportive of people who espouse their various opinions (no matter how foolish), we are far less supportive about butchering facts – especially when the only reason for putting the content on the web in the first place is to make a couple of bucks. With that in mind, we suggest that you have a look at the Hunker.com post entitled "How to Read Screw Sizes" and decide what you think of our DotD candidate Jess Kroll.

Kroll's MFA in writing notwithstanding, we suspect his familiarity with screws was about that of the average middle-schooler who hasn't taken a shop class. We base that assessment on his introduction, in which he lists a few of what he thinks are screw sizes¹:

"Sequences like '4-30 x .10,' '1/8-10 x 4/6' and 'M5-.4 x 15' may seem meaningless, but they say a lot, and you need the right screw to do the job."

In the first place, you need to know a lot more than the screw size to choose the "right screw to do the job"; and in the second, some of those "sequences" not only "may seem meaningless," they are meaningless! What screw has ever had a length of 4/6? No, Jess apparently just threw some numbers and letters at the page to bamboozle the eHow content editor, collected his stipend, and laughed into his black turtleneck (he's a poet).
According to Jess, that first "sequence" can be decoded like this:

"...first letter of the size... the largest diameter: the measurement of the screw on the thread... 4-30 x .10 has a major diameter of 0.112 [inches]... 4-30 x .10 has 30 threads per inch... Metric threads display the millimeters per thread...the third number... is the length of the screw."

For one thing, Jess, "4" is not a letter. For another, "the screw on the thread" doesn't make sense; what does make sense is "the thread on the screw." Next, a thread count of 30 TPI is non-standard; thread counts are almost always multiples of 4. We think "millimeters per thread" is a somewhat clumsy way to say, "distance between threads in mm," ourselves. Finally, while Kroll is correct in saying that the last number is the length, we've never heard of a screw ¹⁄₁₀ inch long.

Jess also hosed other specs for screws, claiming that,

"Screws larger than 10 are listed as fractions of an inch. For example: 1/8-10 x 4/6 has a major diameter of 1/8th of an inch."

The "larger than 10" holds true only for (some) machine screws; wood screws come in sizes to 14 as do many machine screws. Oh, and we're nonplussed, to say the least, that anyone would claim a screw has a length of "4/6"! That's not to mention that a #10 machine screw is ³⁄₁₆" in diameter...
No, it's patently obvious that an ignorant Dumbass of the Day tried to reword information he didn't understand, and that's why Kroll made such a mess of it.

¹ We won't bother to point out that Jess only addresses machine screws, ignoring sheet metal screws, drywall screws, construction screws, wood screws, etc., in his ignorance.

copyright © 2019-2022 scmrak

DD - FASTENERS