Shop stock of metric hardware

I’d like to stock a bit of small metric hardware in my shop for use on 3d printers and related projects. I went to bolts depot and found that there are clearly more sizes and types of M2 -M6 hardware that I have any reason to stock.

I’d like to narrow things down a bit. I like button head bolts because they seat flat against flat parts. I also see a lot of hex socket head screws/bolts - often with ridges around the cap. I don’t understand the benefit of these over button-heads.

Beyond the types of bolts, I’m like to identify good sizes to have. M2 is pretty small, but may be handly. M3 - M5 seem the most useful. What lengths are most often used? I don’t expect I’m use many long thin bolts just as I doubt I’ll need lots of short fatties.

Anyway, I know I can buy random assortments on amazon, but I’d rather buy someplace like bolts depot and pick up a 100 pieces each of maybe a couple dozen popular sizes so I can build projects without knowing that I’ll need to make a 1.5hr trip to a hardware store.

I stock wood screws and that’s worked well. I keep a stock of sizes from 5/8 to 3 1/2”. The biggest portion are 2 1/2 and 1 1/2 since most of my wood projects are built with 2x4, 2x6, and 3/4” plywood.

I’d like to do something similar for 3d printers and similar projects.


I’m overthinking this. I’m going to order some assortments, with a focus on M3, but at least some M2, M4, and M5. I have a box of M2.5 (for the MPCNC) and tiny (snortable?) screws for laptops.


No such thing as overthinking :wink:

M3 is probably the most common size I have seen on 3d-printed stuff. NEMA17 motors use them, fan shrouds, PCB standoffs, etc. Aside from the already mentioned limit switch fasteners I don’t know of any other common use for M2.5 and for self-tapping into printed parts screws that small probably won’t hold all that well. M4/M5 are used with Openbuilds-type aluminum extrusions and T-nuts, M6+ are pretty hefty (and $$) parts and you probably won’t have lots of uses for them.

I’ve got pretty much the assortment you are describing and feel pretty well supplied, but when I make another BoltDepot order I’m going to look and see what gaps I might want to fill in.

My dad gave me a couple of tackleboxes full of M3 hardware from 6mm to 45mm. Some washers, nuts, and locknuts. I have used them so often now that I have a 3D printer. A lot of parts are already designed for them, but I also tend to use those in the parts I design because I have so many. They are almost all the socket cap type with allen drive and the knurled caps. They help when hand tightening a little.

I also print a bunch of M3 hex nuts, about 40mm long, 100% infill and I can cut them to the length I need for various standoffs. I have similar spacers. Having a 3D printer isn’t worth it just to print spacers, but it is really nice to have!


I hate allen head bolts because I can never find the key that goes with it, or even if I have the key, I have to try several times before I find the right one because I can’t tell from looking what size it takes. My printer drove me crazy while building it because it used multiple slightly different sizes when one size would have worked fine.

If I were stocking allen head bolts I would pick one size and never use anything else and just use more of them if I need a stronger hold. Or at the very least use sizes that are so obviously different that you can pick out the right allen key even when half asleep.

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I normally like Allen key bolts, however I have found two issues:

  1. The heads are normally higher than normal hex heads. This can cause problems with clearances, certainly on two areas on the Z axis MPCNC (ask me how I know).

  2. You need to have a more or less straight on access to them to tighten and undo them, a head head allows side access as well. I know you can have a L shaped allen key but that still has some length. You can also use ball headed Allen keys to give you a slightly different angle of attach. You need to make sure you buy these though as most Allen keys are straights. I use the Wera ones from Germany and they are top notch. If I had unlimited budget I’d go Swiss Tools.

I get round the which size it is with colour coded bits on them. I find the same issues with hex nuts so thats not a benefit or drawback to me.

I find I have to buy them in sets of M3, M4 and M5 to get a reasonable range otherwise the costs of a bag of 12mm, and 16mm and 20mm and 25mm etc etc gets too expensive.

Quality seems pretty much the same for non critical applications. I haven’t seen anything bad for MY applications. I’m not launching aircraft of rockets though :slight_smile:

What annoys me is that my late father imported these metric bolts by the 10,000’s around 20 years ago and I could have filled my boots but didn’t and then they sold the business.

Best of luck


That’s okay, most of the aircraft I worked on use phillips, or high torque screws. High torques are weird, they look like phillips, but the cross is offset.

And we won’t even get into the difference between Phillips and the JIS cross screws. I was at the receiving end of more stripped JIS screws on Japanese motorcycles due to the owners trying to use a Phillips screwdriver. Phillips are rounded in the center and JIS are not. A JIS screwdriver works on both, but the opposite isn’t true.
Oh wait, I did get into it. :slight_smile:

Oh, and then you had these pieces of shit.s-l400 (1)

Those are coin screws! Not sure why they exist.

I get to work a night shift where I wait some odd hours for some contractors to do their job before I put in my 15 min. Probably as good a time as any to buy hardware and hardware assortments.


Never even seen those before. They look weird!

They’re also high torque screws, have a driver that looks like a fat pizza cutter. Also used on aircraft. They’re really good at screwing up the paint all around them from the driver slipping out…


Finally ordered hardware! My draft order at boltdepot came out to around $300, so I decided to buy several assortments on amazon instead for about $100.

Got Hex socket M3-M5 in flat (countersink type) button and socket-cap types. I got an assortment of M2 as well. Maybe I’ll use them, maybe not.

Boltdepot does seem to have good prices though. I ordered nuts and washers there. When I figure out what sizes I use most, I’ll definitely reorder there.

Boldtepot is really good price wise if you need 100+ of something or 1-5 of something. Most in-between cases might be best served with assortments you can get on Amazon or locally.