So you need to drive a metric screw into plastic, wood or sheet metal, but there isn’t a threaded hole where you’d normally need one? Well, if you have the right screw, there’s no need to spend valuable time setting up a tap to create female-threaded holes precisely mated to the screws you want to use. A thread-forming screw will make its own threads as you drive it into the material. Problem solved!

How do thread-forming screws work? Thread-forming screws and thread-cutting screws are two varieties of a category known as self-tapping screws — that is to say, screws that basically force the substrate to mate with their threads. But unlike thread-cutting screws, which remove bits of the material as they carve their way into the substrate, thread-forming screws deform the material, bending it into a mating position without actually removing any of it. The type of screw you require depends mainly on the type of material that will be wrapping itself around the threads. At Mr. Metric they offer metric thread-forming screws suitable for either plastic and wood substrates or for sheet metal, tubular metal and other lightweight metals.

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Solving fastening problems is about controlling variables or eliminating potential causes that create an unwanted fastening event. Let’s take a look at common unwanted fastening events. Cross threading, thread or component stripping, unseated fasteners, missing screw, nut or bolt (omissions) these are all evident events of failure that we can see with our eyes. Thank goodness for our eyesight, because these are easily recognized. Fastening problems that we cannot see are our biggest risk. Latent failure can be a big problem depending on the product or exposure to risk or liability. Latent failure is caused not only by under torque, but largely by over torque events. Most all of us have opened a product package and discovered a screw or nut that came loose in transit. We might have also found one on the floorboard of our car. Many times these screws or nuts are not critical, they may come from the exterior of a product.  However, they still concern us. They should.  It makes us wonder if something more critical might also fail. Every time we find one of these rogue fasteners something did not go as planned, thus a torque related problem or unwanted fastening event has occurred. These occurrences are frustrating, time consuming and many times create delay and cost. You can get rid of them!

Let’s not overcomplicate things when we study fastening variables. In our experience there is only a handful of really complicated fastening problems and most of our customers don’t experience many of these all that often. Generally, it is a simple set of variables that need to be discovered, isolated and removed to solve fastening related headaches. It’s important to thoroughly investigate in a scientific manner  what may be wrong with the fastening scenario. More important is not to freak out and think that everything is wrong, and try to change too many things too fast. The process of elimination is a great tool for solving fastening failure. Fasteners are generally made to a specification that defines physical criteria. The information is public and validating dimensions is not hard. You can do it on line or in most any hand book.  

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Do your eyes glaze over at all the metric bolt choices? We know it can be kind of confusing, especially if you’re not used to ordering metric parts. Let’s look at the meaning of some common terms in the world of “bolt-ology.”

Bolts have different heads that identify their use for different applications. Hex bolts, for instance are simply bolts that have a hexagonal, or six-sided shape to their head. These bolts may have threads extending either halfway or all the way down the shaft and generally require nuts and washers to hold themselves in place. Flange bolts are instantly identifiable by a flat flange that somewhat resembles a washer peeking out from underneath the head but is actually part of the head itself. The flange grips onto the substrate and distributes the clamping force across it just as a washer would, saving you the need for that separate part.

How do we assign measurements to metric bolts? The bolts in our catalog are all identified by the letter M (for “metric”) followed by a pair of numbers. The number immediately following the “M” indicates the diameter of the bolt

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Metric spring pins provide extra security in parts of assemblies prone to frequent jolts or vibration. Ordinary dowel pins or other metric fasteners can respond to these disturbances by coming loose and eventually wiggling out of their shafts. A spring pin, however, produces some force of its own to counteract those outside forces. It actually exerts pressure radially, pushing against the walls of the shaft to keep itself securely in place.

There are two basic varieties of metric spring pins, coiled spring pins and slotted spring pins. Coiled spring pins are fashioned out of a flat strip of steel rolled into a cylinder so that if you look down at it from one end, you see a spiral pattern. How does this construction allow it to exert radial force outward into the shaft it’s driven into? Well, the pin’s diameter is actually slightly larger than the shaft — the ends have to be rounded or chamfered to help the pin force its way in.

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