Trying to find out what screw thread is used to fix hard disc drives into a PC chassis. I've sent an email to Seagate, but no reply so far. It seems a simple question but I just can't find the answer on the net. I do know that the thread is not the same as regular PC chassis screws even though the screw looks similar. Anyone know for sure?
I've got several disks here. Perhaps they aren't the same model but I'll tell you what these use. All screw holes for mounting are standard #6-32. This makes sense because the casting is aluminum. You wouldn't want a finer thread than that into aluminum.
Thanks for the replies - US 6/32 The reason I need the thread is that I'm fitting HDDs into a custom carrier made from thick Al for heatsinking. The screws supplied with each HDD are not long enough, so I have to source ones a bit longer, ideally with countersink heads.
It depends. There are two standards. 6-32UNC, and M3. Historically, drives made for the US market, had the former, while those made for the European/Japanese market had the later. You can even get the same drive, with both thread types from some manufacturers. I had 'joy' a few years ago, when having to source replacement drives in quantity, and the only ones available at the time, had the metric threads, where the originals sourced via the US, had the imperial threads... Generally 6-32, is the more common fitting on the 3.5" drives.
In soft materials, you get greater ultimate strength using a coarse thread. This is why the 'standard', is to use coarse threads in soft alloys, and finer threads in harder materials. You can cut a fine thread, but for structural strength you want it coarser. Historically, the old 'Whitworth' threads, were the result of quite a lot of research, trying different tooth shapes and pitches, to maximise strength in soft materials, and the UNC threads, are very close indeed to the same (in general, just changed the tooth shape to a 60 degree form, that is slightly easier to machine, than the 55 degree shape used on the Whit threads). The 'standard' metric thread (unless a pitch is specified), is actually the coarser of the metric normal forms, being reasonable for harder alloys, but rather too fine for soft aluminium. Stupidly, this is used as being 'easy' in a lot of places, despite it being less than optimal. If you look at the studs used on PC cases, those made by 'better' manufacturers, have a coarse thread on the stud designed to screw into the alloy case, and a finer thread on the inside to take the screw (cheaper manufacturers don't bother, and use the same thread on both parts...). Fortunately, in general, the actual strength needed in PC parts, is tiny, compared to the ultimate strength, so people 'get away' with poor thread selection.
Here in Australia, things are dicier still. I've got two identical Seagate
7200.10 drives, bought a couple of months apart from different vendors. One uses 6-32 screws, the other uses M3's. I've recently bought a few Samsung
501LJ's and they all use M3's. The older SCSI drives I've got use 6-32's. Self-tappers and a strong screwdriver are starting to look enticing :)
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