The M3 screw has an actual diameter of around 2.9 mm, while the diameter of an M2.5 screw is 2.4 mm, and that of an M2 screw is 1.9 mm. This is the only difference between these three screws. This depends on the manufacturer you buy from. Some brands might provide screws to fit the drive into its slow. Gigabyte usually has the screws already screwed on the motherboard, while others like Dell (such as with the Inspiron 3670) don’t include the screw or even the post into which the screw fits. It only has a hole for the screw needed to install the drive. Instead, the screws for mounting the SSD come with the motherboard or the mounting kit you’re planning to install it in. – Why Don’t Some SSDs Come With the Screw? Each screw size is described using two numbers – the ‘M’ number and a number indicating the length of the shank, in mm, so M2 screw dimensions of M2 x8, are 8mm long, measured under the screw head. Sorry about the late reply, but I ran into the same issue and looked up the info, so thought I'd drop a useful answer since nobody gave the best one:

Missing a screw for your M.2 SSD? Check this out! Missing a screw for your M.2 SSD? Check this out!

Hi, So I recently bought my first SSD. The 970 EVO. However, I have no screw to place it. It's not on the motherboard, it did not came with the SSD and the box of the Mobo is lost... I can't seem to find them anywhere online, except if I pay 15 euro and wait 3 weeks until it comes in. Does anybody know which screws I need exactly? So I could try hitting up some hardware stores to see if they have some? Each M2 is described using two numbers – a digit with the ‘M’ and another number that indicates the shank’s length in mm. So, for instance, if you see a screw with dimensions M2 x8, that means the diameter is 2 mm, and the length of the screw from under its head is 8 mm. It’ll have a table of contents that’ll most likely tell you where the M.2 screw is and show you what it looks like.Ryzen 9 5900x | Full Custom Water Loop | Asus Crosshair VIII Hero (Wi-Fi) | RTX 3090 Founders | Ballistix 32gb 16-18-18-36 3600mhz Not sure if your board has the standoffs or not. Mine did not, but others I have DID have the standoff and screw included. My old one might have had it in box at one point, and I just didn't need it at the time and lost it. Yea the M.2 screw is usually just in a little bag, included in the motherboard. They really should be just installed, by default, for less plastic waste, though. So there’s a non-zero chance that there might be a screw that could fit an M.2 standoff in your collection.

M.2 SSD Scew Will not Fit - Hardware Hangout - Neowin M.2 SSD Scew Will not Fit - Hardware Hangout - Neowin

Keep in mind that "M2" is a common screw size measurement used for all sorts of components in laptops. On the other hand, "M.2" (with a period character in it) refers to the connectors and their associated hardware for SSDs, Wi-Fi cards and similar slotted devices. Take a look under his and at 2:27. There is a small bag where you can see the standoff and screw. Then again at 3:25

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Another important measurement is the pitch, which is the distance between the threads. An M2 screw has a standard pitch of 0.4 mm, but you might need a screw with a non-standard pitch depending on your motherboard and SSD. M2 screws are available in a wide range of materials including steel, stainless steel, brass, nylon, aluminium and titanium as well as exotic materials including Duplex, Super Duplex and Inconel. So give it a search and see if you can find something. You probably won’t find something perfect, but even a close enough fit is fine. Xeon X5560 - RX 570 4GB (defective) - Fattydove Racing 240GB - WD Blue 320GB - HP Z400 - 6x2GB DDR3 1066 - EVGA 450W3