How to choose a metric screw assortment kit
A metric screw assortment kit is only useful if it carries the sizes your repairs actually use. Here is how we decide what goes into a Hapric box, and how to pick the one that matches your bench.
Start with the diameter the job uses
Electronics, drones, cameras and most RC gear run on M2 and M2.5 machine screws. 3D printers, robotics kits and appliance control panels are overwhelmingly M3. M4 and M5 show up on brackets, bike racks and printer frames. Furniture, fitness equipment and engine covers live at M6 and M8, and M10 is motorcycle and trailer territory; M12 and up is structural and belongs in a different drawer.
If one of those describes most of your work, a single-size kit is the cheapest way to get eight lengths of it with hex nuts and washers. If the bench sees a little of everything, our 2,160-piece M2 to M6 kit carries twenty sizes in one box.
Lengths that matter more than counts
A big piece count means nothing if the lengths are wrong. For each diameter the useful range is narrow: M3 from 6 to 30 mm, M5 and M6 from 8 to 35 mm, M8 from 16 to 50 mm. We cut our kits to those ranges in steps of 2 to 5 mm, which is why a 600-piece M3 case solves more problems than a 2,000-piece grab bag of random hardware.
Socket head, not pan head
Most cheap assortments carry Phillips pan head machine screws because they are cheap to make. We cut hex socket head screws instead: the key sits inside the head and cannot cam out, so the screw survives being driven and removed dozens of times, and the low cylindrical head fits recessed holes in printers and appliance panels. The matching hex key comes in the box.
12.9 alloy steel or 304 stainless steel
12.9 is the strength class: about 1,200 MPa tensile, the strongest common grade for a socket-head screw. Under black zinc it is the right choice for dry indoor work and anything that carries load. 304 stainless steel gives up some strength for corrosion resistance and needs no coating, so it belongs in bathrooms, kitchens, boats and outdoor frames. Our M2 kits come in both, and the 1,660-piece kit ships both side by side.
Hex nuts, washers and the key in the lid
A screw alone is half a joint. Every Hapric screw kit adds a hex nut per screw and flat washers; the M2.5, M5, M6 and master kits add split lock washers for joints that vibrate. The hex key is cut to the kit's socket and the tweezers handle M2 and M2.5, so the box is the complete tool for that size.
The last check is the container itself. Thick fixed dividers and labels inside and out are the difference between a kit that is still sorted after a year and a bag of mixed hardware.
