I been puzzling, tossing and turning at night about: What did they base screw sizes on? It ain't gauge - a #6 screw would be huge! - it ain't the military method where a #6 would be 6/16ths so what the hell is that stuff based on? And, is a #6 sheetmetal screw the same diameter as a #6 machine screw? Can you use a drill bit to tap and thread for a #6 machine screw and use it for drilling sheetmetal for #6 sheetmetal screw? What the hell happened to #12 screws? Where did they go? It ain't the same as 3/16ths, i got different taps for each and they are a little different. As far as that goes what happened to 3/16ths? ever find one of them screws at the hardware store?..seems like the only place they are used is in a ******* toggle bolt! Be aware i am using #6 as an example only. How about enlightening me and share your knowledge on screwing knowhow?
I haven't got any answers for you but I'm very curious to hear the answer to your question. Screw sizes are strange to me...
I think it was The Society Of Automotive Engineers back in early 1900s that standardized the sizes of the thread sizes and many other materials we use today. Jim.T.
<LI cl***="step " itxtNodeId="7" itxtHarvested="0">1 Place the shank of the screw between the jaws of calipers that can measure to thousandths of an inch. Adjust the calipers to read the diameter in inches, expressed to three decimal places, such as .177 inches. <LI cl***="step " itxtNodeId="6" itxtHarvested="0">2 Subtract .06 from the measurement. <LI cl***=googleAd itxtNodeId="5" itxtHarvested="0"> <LI cl***="step " itxtNodeId="4" itxtHarvested="0">3 Divide the result by 13 and multiply by 1,000 to find the gauge of the screw. For example, .177 minus .06 is .117. Divide .117 by 13 to get .009, then multiply by 1,000 to calculate that you've measured a screw with a gauge number of 9. Read more: How to Determine the Gauge of Screws | eHow.com http://www.ehow.com/how_7461296_determine-gauge-screws.html#ixzz24qY3mz12 OJ, Now you can stay awake all night figureing out how they came up with this fine idea!
If I didn't have a ref. chart, often you can take a machinist's caliper to find the screw's root dia, and use the next step larger drill dia. for thread pilot holes. Judgment req. your results may vary!
#6, 8, 10 and 12 machine screws are measured in 32's of an inch, i.e 6/32, 8/32, 10/32. AN fittings such as #6, #8 or #10 are measured in 16ths, so a #8 would be for a 1/2 inch line or hose. The specifications come from differnt standards, one is ASME as provided in Mooses posting above and the other is the Army Navy Standard (AN). There are other hardware standards such as Military Specification (Mil Spec or MS). A very good explanation of hardware, specifically aircraft hardware is provided in an FAA Advisory circular, AC 65-9. The do***ent can be purchased for around $20 or downloaded from the FAA webpage as a pdf file. http://www.faa.gov/regulations_poli.../index.cfm/go/do***ent.list/parentTopicID/121
I use this method for sheet metal screws but in the case of machine screws I have a big "decimal equivalent" chart hanging on the wall which lists tap drill sizes for all machine and pipe threads.
Why ? Man that's screwed up Sheet steel and wire size gets thinner as the number goes up. That's because the number coressponds to the number of p***es thru the drawing dies. The more p***es, the higher the number and thinner. That has nothing to do with screw size but its a hell of a lot of better than a bunny with a pancake on its head
LMFAO, I thought you meant "screw sizes!!!" and I was going to say, hell yea screw 'em all. A #6 sheet metal screw and a #6 machine screw have the same shaft size according to my machinists hand book. If you are going to be sticking it into sheet metal you should be able to get way with the same drill size of one a letter smaller. But if you are going to stick it in a piece of plate or what have you and you are going to have to tap it you should adhere to the rules for tapping threads, it would take a different size drill because of the co****ness and pitch of the thread. I have no idea where they came up with the numbers for sizes, but I still don't know what an AN fitting is called a dash # either.
This is giving you sleepless nights? No offense, but I'll trade your problems for mine anyday. Why do we drive on the parkway and park in the driveway? What is the opposite of "ruthless"? Why do reckless drivers have so many wrecks?
Note that the #12 is pretty close to 3/16 (especially the fine thread version.) However, in my collection of taps, which includes stuff from a variety of sources, there IS one labelled 3/16 but it carries no pitch number. My pitch gage says it is a 24 tpi. Further my thread/tapdrill chart (which dates to the '60s) shows #12 as 24 & 28 pitch. The chart posted here shows 24 & 32.
WRONG. The 32 in those designations is the number of threads per inch. Think about it: If a #6 was 6/32" in diameter it would be 3/16" which it ain't-it's actually .138" or about 9/64. A #10, id it was 10/32" in diameter would be 5/16" or .312. Actual for a #10 is .190 (the modern replacement for a 3/16).
Did you ever ponder how shotgun gauge sizes were determined? I think it has to to with the number of balls of some standard diameter (?) which will p*** thru the inside diameter of the barrel.
So 10-32 is ten times .031? Or .310 thousandths? 5/16 of an inch? Maybe not. Maybe 10-32 means a number ten screw with 32 threads per inch. And a 10-24 will be the same diameter but with 24 threads per inch. How they came up with the numbers is something I never thought about. Don't think I will think much about it in the future.
Too much thought... there are standard nominal diameters for #2 to #10 screws, .086 all the way to .190, from 1/4 & up it goes by the pure fraction value. I just have a running tap & drill chart in my head for regular and form taps as well as STI (helicoil) drills. I can calculate almost any oddball tap drill quickly. Bob
what is real cool is buying a no. 8 0r 10 with a no. 6 head works great when stock holes are enlarged and you can match heads. just a little more **** in the game
I read this thread and I have always been curious about the answer but for some reason my eyes are glazing over. I'll check back later when it is all sorted out, I guess.
Often wondered myself. I use this nut & bolt gauge to determine the size drill bit to use. It measure down to size 6. Thought about making a bolt screw gauge for smaller sizes.
yeah , screw sizes are screwy...so are wire gauge size and sheet metal gauge sizes but , i've been messing with stuff for 50+ years and i'm used to them
You will have to look up S.A.E.. Back when people were making there own autos and machinery they were making there own diameters and thread amounts per inch, a group of engineers S.A.E. realized we needed to have the same size for all bolt sizes and oils and many other things in the auto industry.
<LI cl***="step " itxtHarvested="0" itxtNodeId="4">Or, coming at it from the other direction, if you'll multiply the screw size (#8 for instance) by .013, and then add .060 to that, you'll get the nominal body diameter of the screw, or minimum clearance hole size. #8 X .013= .104 + .060= .164 dia.
Im kinda surprised no one has mentioned the use of Clutch Head or Roberts Head. Clutch heads were,and maybe still are used on the inside of Holley carbs,& Roberts were used alot on early campers & Rvs. Clutch heads use a small bow-tie shaped driver,while Roberts take basically a small square driver....screwy
Makes perfect sense to me but I was an aircraft machinist for 15 years and still do quite a bit of machine work in my shop at home. I started doing machine work in 1982 and still enjoy it though I wouldn't want to do it for a living anymore. P&B mentioned the Machinery Handbook; i fyou ever get a chance to snag one jump on it. That thing has everything you ever need to know about machine work.
Now, this is just 'screwey' enough that i believe it - i wonder where the '13' came from in the theorm. I kept waiting for the explanation that the gauges corresponded to a particular set of holes in a Roman Chariot and the screw had to p*** thru the set of holes made by Gauge Constantinople the master chariot maker, hence the term 'gauge'.
All of the above would never have helped me when I had my helper put away several boxes of nuts a long time ago. He paced all of the light silver ones in one jar and the brownish ones in another. Some of them were plain steel, so they went into another jar. All the screws went into one larger jar.
The Jalopy Journal
