All Screwing All The Time

May 30, 2021 7:21 AM

I need to up my game when it comes to knowledge about mechanical fasteners. I would like recommendations for more academic resources, please.

Short Question:
So I'm handy in a really broad proficient way. I make and fix all kinds of things right and left, but there are quite a few things I really don't understand fully and think I'd like to read about screws and mechanical fasteners from a mechanical engineer's point of view. I want to know everything from terms and definitions to use and strength. I don't need to be entertained. I need to fundamentally understand and express that understanding.

Is there a textbook that defines it all that you'd recommend? I am googling specific questions as I have them, but it is piecemeal work and I thought I would reach out for something here.

Longer Question with backstory:
I'm one of those people who can build almost anything, but I just *sense* which fasteners I need to use based on extant project parts, previous experience, educated guesswork, experimentation, and... I don't know... universal consciousness? I understand the basics of things - Phillips v. Standard, wood v. machine, screw v. bolt, and some basic things around there, but it gets hard to go into (especially rural) hardware stores and supply houses and voice what I need.

This in turn tends to make the guys helping me treat me like an idiot and a sissy - or worse. I may very well be both of those things, but I really hate coming back from a supply run feeling like I just got owned by the captain of the football team or disappointed my Dad. It is a real bummer of a feeling on my end and that's when they are at least being polite and trying to be professional. It really a downer if they are helping because they have to but are hostile.

SO... I want to be able to walk in and say "I need a 2" brass eye bolt that is 10/24 (or whatever)" instead of "I have this piece I need to connect to this other thing to join them with this other thing" and then dump a bunch of stuff on the counter as they sigh and roll their eyes. This would also save time because I won't have to explain the project and have their uninvited input on that as well.

At big box stores, there is a lot of shrugging and pointing without knowing exactly what I am asking and I have to figure it out on my own anyway.

I'd ideally like to be able to pull something apart, look at the fasteners, and be able to confidently add the type and thread to a list without needing to haul them around for a painful show and tell or a safari through the fastener aisle. I'd like to design and build something and understand fundamentally why I should use this or that rather than just walk around until something in the aisle looks/feels right.

So there we go. Help me learn about fasteners so my days are less ruined when I am working on cool projects, unassisted fastener shopping goes faster, I can confidently design things with less experimentation, and fully understand the why something was used.

posted by Tchad to Education (13 answers total)

One step would be to get a "thread checker" or "thread size identifier". Then you can at least figure out the thread on whatever bolt or hole you are trying to match. There is often one available at the store, but you can buy them and use at home so you don't have to lug the whole part to the store.
posted by yuwtze at 7:56 AM on May 30, 2021 [3 favorites]

I know you said you didn’t want to be entertained, but this sounds like a YouTube problem. I just searched YouTube for mechanical fasteners, and there are lots of videos — it’s not the textbook you were thinking of, but watching a bunch of videos should give you not just information, but also how handy people who know this stuff talk about it, which seems as if it should help you when you’re trying to communicate without feeling ignorant.
posted by LizardBreath at 8:06 AM on May 30, 2021 [3 favorites]

I find the best way to learn what a discipline teaches is to examine the trade's catalogs.

McMaster is a pretty comprehensive "if it exists, it's listed somewhere" in this catalog. You will learn a lot of nomenclature and standards of fasteners by browsing around. I'd recommend the same thing for electronic design by examining the DigiKey catalog.
posted by sydnius at 8:23 AM on May 30, 2021 [13 favorites]

Best answer: The weirdly named "machinery's handbook" is a classic.

A thread gauge or screw thread identifier plate (in both imperial and metric, if you're in the US) and a set of decent calipers, with hole center finders if you want to be fancy, are worth a lot when it comes to figuring out what the thing you already have *is.*

As a non-engineer who spends a lot of time talking to machinists and fabricating things, my sense is the usual answer when designing new things is "there are thirty equally good options. This one's cheap, over-specified, and McMaster will send it to us tomorrow, so let's use it."
posted by eotvos at 8:25 AM on May 30, 2021 [8 favorites]

Best answer: I use an old-school Screw Chart and a digital caliper to identify common fasteners. Note that diameters will measure small on many mass produced threads. If you have both the screw and nut it is easy to calculate thread pitch by measuring the change in thread engagement and dividing by the number of turns. I find the slide chart faster than and app or my beloved/dogeared Machinery's Handbook.

I was also going to recommend browsing McMaster-Carr (search "fasteners" for a picture index), their search is wonderful but for the tricky stuff I sometimes need click the "view catalog page" option on the top right
posted by tinker at 8:37 AM on May 30, 2021 [1 favorite]

Digital calipers are surprisingly inexpensive -- mine will even give metric or fractions of an inch -- and saying "I need to replace the 11/64ths star bit screw for an old microwave" gives you a stupid amount of gravitas.
posted by amtho at 9:04 AM on May 30, 2021 [1 favorite]

Oh - and 'It needs to be at least 1/2" but no more than 11/16" ' is great too.
posted by amtho at 9:06 AM on May 30, 2021 [2 favorites]

Seconding McMaster-Carr. It has pictures and you can drill down until you find what you need. Generally you need to consider metric or imperial, diameter (outside size of threads), pitch (normally there is only coarse and fine for a given diameter), length (generally measured from under the head except for flathead, ie wood screws), drive type (phillips, hex, Allen, slotted), and head shape (flat, pan head, round head, filister, cheese head, there are more but these are the most common). I cheap set of calipers, a ruler, and a thread pitch gauge are the tools of a pro.

The nomenclature is generally the thread size and pitch followed by the length and head. If I know what I want at the hardware store I will say, "I need a 10-24 x 1/2" pan head, stainless steel screw" In metric it would be, "I need an "M5(diameter) x 1.25(pitch), 25mm long with a hex head."
posted by Grumpy old geek at 10:50 AM on May 30, 2021 [3 favorites]

Best answer: Machinery's Handbook and a set of calipers and you're covered. Now, because I can be lazy sometimes I bookmark some online size charts and screw company catalogs (to get head details), but those don't include the whole spec and backstory and everything like Machinery's Handbook does. They'll also let you know what the strength specs are for grade 5 and grade 8 bolts, and for literally everything else.

#6 is .138
#8 is .164
#10 is .190
Anything above that the basic size is the decimal value of the fraction (1/4 = .250); anything smaller than that you still have to look up. Everybody uses coarse thread most of the time, except sometimes people use #10-32 which is fine thread. Anything metric, the number after the M is the basic size. Nobody else in America knows which pitch is default for a metric size either.
posted by Huffy Puffy at 1:03 PM on May 30, 2021 [2 favorites]

Best answer: The detailed mechanics of fasteners is incredibly complex. The static strength of materials part is the simplest, but on top of that there's elastic/plastic deformation and a whole heap of weird factors like surface treatments/tribology that determine whether a thread will stick or slip. Consequently, most design work is standards and table based so that you do a relatively simple calculation, then look up part sizes on a table based on your application. Don't forget that fasteners can be quite expensive, so modern design does as much as possible to minimize their use.

For identifying parts, a digital caliper (even a cheap one) will be the best first investment. A decent engineer's rule is worthwhile, too. If you can swing the cost of thread gauges, they'll save time. For sizing charts, Machinery's Handbook is overkill. It's also a deeply odd book if you learned to design from ISO standards: Machinery's assumes that working with weird American units as normal, then introduces metric as a further complexity.

Metric screw fasteners almost universally use coarse threading. They also tend to use a few preferred sizes, so rather than going up in diameter increments, they go in a geometric series. If you're replicating/repairing something made outside the USA, it'll be metric throughout. Note that sizes less than M6 are not often stocked in big box hardware stores in N America.

The McMaster Carr catalogue approach to specifying things is a good one: the what (machine screw/sheet metal screw/wood screw/eyebolt/carriage bolt) followed by the material/surface (plated steel/stainless/brass/bronze) followed by head type (hex/cap/Robertson), then diameter, thread pitch, length and finally quantity. Sometimes you'll find trade counter folks who enjoy being an arse to their non-regulars and will quibble every tiny mis-specification: go elsewhere the next time if you can. It pains me, but Amazon is amazing for sourcing fasteners.

Big box stores have a very samey selection of fasteners. Home Depot owns several of the major distributors, so their stores all have near-identical fastener sections. The bin numbers in Home Depot stores are the same across the USA and Canada, btw. Availability of fasteners can be highly regional, too: if you're in or near auto manufacturing, a whole world of metric fasteners awaits you. If you're stuck in Ontario like me, everything that isn't a machine screw has a Robertson head on it in the big box stores.

If you're in rural USA, TSC and especially ACE Hardware can have amazing selections. An ACE in a small town in Ohio had a better selection than some of the specialist trade counters I've used in large cities in Canada.
posted by scruss at 11:33 AM on May 31, 2021 [1 favorite]

Best answer: Engineer here who has to deal with the technical ins and outs of threads and fasteners on a daily basis. My go-to reference is the Machinery's Handbook referenced a couple times above.

For my purposes calipers are not accurate enough. I use a micrometer in conjunction with thread wires to determine pitch diameter. The pitch diameter is crucial for fasteners; we almost never have to worry about major/minor diameter. Pitch diameter is where things get messed up.
posted by spikeleemajortomdickandharryconnickjrmints at 10:57 AM on June 1, 2021 [1 favorite]

Hey, I'm sorry -- I have no answers for you but had to convey how much I loved your subject/title. Bravo!
posted by zenpop at 1:17 PM on June 1, 2021

Response by poster: Thank you all so SO much!. Your input made me look through what's left of my grandpa's machine shop and I found a 1979 copy of Machinery's Handbook as well as a couple of gauges and some calipers. That should work well for the kinds of things I do which require technology not much past 1950 or so.

Between that and studying McMaster-Carr's site, I should have plenty to bite into and really take some time to get a better basic understanding this Summer!
posted by Tchad at 1:28 PM on June 3, 2021