Kevin Moorcroft, M.D. here at industrial threaded fastener specialists Challenge (Europe) Ltd recently discussed the question – What screw head type should I use? – with some helpful tips as he explained: “Standard hexagon head is one of the most common form of screw or bolt head used throughout industry in typical sizes from M4 upwards but there are also countersunk screws with recesses of many types, e.g. multi-splined, hexagon socket, pozi and slotted. These have particular purposes since countersunk screws for example finish flush so need a recessed drive. There is also pan head which is effectively surface mounted and tends to be used for M1 up to M8 sizes with many drive forms available.”
For both stock and custom needs in recent years it seems that the tendency has been to avoid slotted drives because they do not lend themselves to power tools, either manually or robotically operated. Consequently a wide variety of other designs have been created primarily to aid fast and accurate machine-driven assembly with less slippage and more control of speed, torque and pressure.
Standard external hexagon drives suit many kinds of automated assembly, these and hex socket drives are both very positive options for larger sizes. However, auto-feed tooling is required for high speed assembly and this presents the screw to the driver which best utilises multi-spline recessed heads for fast positive performance.
Socket head cap screws are a good example of a screw design suitable for manual or semi-automated production and feature an internal hex drive in a circular head, often with external knurled finish which aids manual starting of the thread allowing a good finger grip for positioning. Similarly, flange head bolts which have a flange that stands in place of a washer to spread the load. A related variant is the range of socket set screws (grub screws) with internal hex drive, which are used for location, e.g. collars on shafts and similar.
Carriage bolts are a good example of a very useful and specialist head type, in this case very popular with the construction industry. They are formed as a dome with square underneath designed to locate into a square hole in metal or to pull down and lock into wood. This enables the bolt to be tamper proof on the head side and for the nut to be done up/undone without needing a tool at both ends of the bolt/assembly.
Metric thread forms are common across a significant range of fastener products, so that for example an M5 thread is the same irrespective of the head type or screw style. There are of course fine thread, extra fine thread and constant pitch series, but if possible these are to be avoided as their stocked range is not as comprehensive as it is for your more general coarse pitch threads.
Challenge (Europe) Ltd M.D. Kevin Moorcroft explained that “the coarse pitch series of threads will meet most general engineering requirements so these are the standard production and ex-stock items. The more specialist threads such as an M10 fine pitch socket head cap screw, may be stocked by specialists such as ourselves here at Challenge Europe but of course the finer pitch thread forms can come at a premium price simply by reason of economies of supply”.
“Similarly for ‘old’ imperial threads such as the B.A. range, once commonly used within electrical equipment, which has seen its availability diminish during the last recession leading to enforced redundancy in many applications. Although demand still exists for the range, only those sizes/types with viable volumes tend to be stocked and available at reasonable pricing. Sizes not commonly stocked can be small batch produced but again at the risk of premium pricing.”
Other thread forms are slightly different – for example self-tapping screws which have a coarser pitch – and were conventionally used in sheet metal work with variants later developed specifically for use in plastics, the latter becoming more commonly known as thread forming screws. Thread forming screws also exist for use in metals and create a finer machine screw type thread by material deformation during insertion, the theory being that a thread forming screw could be removed if required and replaced with a machine screw. Thread cutting screws also exist having a lead in design feature that specifically aids the cutting/removal of material in a similar way to a thread tap.
Thread forming and cutting screws tend to be smaller sizes typically M2 up to M8 – possibly M10 depending on the drive – since security of the drive determines the amount of torque that can be transferred to the screw.
Specials, e.g. self-drilling screws, are another variant available in a several drill point and thread configurations suitable for use in a diverse range of applications and industries.
Many imperial thread sizes are now either obsolete or trending towards obsolescence, prompted by changes in demand patterns from countries such as the USA who are now drifting towards metric products. This increasing globalisation of metric threaded fasteners does not necessarily mean that all variations are commonly available and it remains important that design engineers are careful in their selection. Whether metric or imperial it is always advisable to seek advice and avoid either paying premium prices or creating lifetime availability issues.
The team here at Challenge (Europe) Ltd are well used to this situation and carry extensive stocks of standard sizes of industrial screws – plus a wide experience in supply of non-standard sizes, threads, lengths and materials.
Explained our M.D. Kevin Moorcroft “We find that standard sizes of metric products have grown extensively to compensate for this trend. ISO standards now cover a whole range of products complimentary to old imperial sizes, as well as expanding on the original ranges of metric fasteners, e.g. metric socket head cap screws once only available in 12.9 grade are now offered under the ISO standard in 8.8, 10.9 and 12.9 grades to suit a wider range of applications with varying requirements of tensile strength.”
As you would expect, small diameter screws find applications in areas such as electronic devices, medical equipment and instrumentation, while larger sizes are used in heavy duty applications such as radio masts, large lighting assemblies, machinery etc.
However, head configuration can have an effect on the size of fastener which can be used. For example, one may wish to use a M6 bolt with a hex head but find conventional spanner access limited, consideration could then be given to the use of recessed drives such as a hexagon (socket) or multiple splined variants. A further alternative is to go to a smaller diameter with an upgrade in material specification, although this may require a greater deal of investigation in order to avoid non-preferred diameters such as M7, M9, etc.
A common failing when at the design stage is to assume that smaller diameter threaded products are available in the same lengths as their larger diameter brethren. In general terms, the smaller the diameter then the shorter are the commonly available and stocked lengths. Nothing is impossible and specials can be created but these nearly always come at a premium price. The answer is to consult the experts whenever possible so contact us to check our stock and custom capability.
Threaded fastener systems – nuts, bolts, screws and washers used in manufacturing industry at large are a time served, well developed, reliable and surprisingly sophisticated technology. They are also well known – but it is often not appreciated just how critical it may be to choose exactly the right material and finish. This is where we at Challenge Europe can be of real help.
Manufacturing industry typically requires threaded fasteners in varying grades of steel, stainless steel, copper, brass and aluminium, depending on the installed environment and compatibility with neighbouring substrates.
As explained by Kevin Moorcroft, our M.D.: “The material choice is the most important first step but often just as important is the choice of finish – we offer chemi-black on mild steel, stayblack on stainless steel, zinc plated, chrome plated and nickel plated as standard finishes on many of our fixings.
“We work with design engineers and buyers in all industries to optimise choices and minimise costs so we can ensure highest quality and quickest assembly times for each product.”
Standard products include machine screws, self-tapping and self-drilling screws, as well as machine screw SEMs, thread-forming screws and hammer drive screws.
Contact us to discuss your threaded fastener and fixing needs.
Each manufacturing industry has its own requirements, but all use threaded fasteners – nuts, bolts, screws and washers. Here at Challenge Europe we address these varying applications with experience and technical expertise which can save manufacturers’ time, money and concerns about quality. Industries such as electronics, medical, agricultural, general machinery, instrumentation, marine, and building, all benefit from our careful consideration of the presented specification and supply of quality fasteners.
Each application is different of course as our M.D. Kevin Moorcroft explains: “In many applications the requirement is fairly straightforward and can often be met by a standard item, however it is also quite common to require a higher spec material or different length, different head form, unusual thread length or non-standard finish. That is where we come in to help identify what is needed and to supply at a competitive price. Where something more custom is needed then we can deal with that too; as we can with a range of fastener associated products or, where a threaded system is not suitable, then we can provide a riveting solution”.
Standard products include socket shoulder screws, machine screws, self-drilling screws and hex-headed high tensile bolts. Smaller sizes of many fasteners particularly suit the electronics industry and a range of plastic plugs protect products in transit from ingress of foreign bodies. Korrex plastic nut caps are ideal for outdoor protection.
Contact us to discuss your threaded fastener needs
Our extensive range of threaded fasteners supports our mission to provide standard and bespoke components, along with both technical and supply expertise in sourcing of specialist specifications. Explained Kevin Moorcroft, our M.D., “We aim to help manufacturers specify, source and ensure reliable supply to production facilities. By working as a partner to industries from electronics to agricultural, machines to aerospace, instruments to window frames – we aim to help small, medium and large manufacturers optimise their products and their production processes.”
Standard products include a full range of machine screws, self-drilling, hammer, wood, self-tapping and thread forming screws. High tensile bolts of course feature in many formats, along with construction floor anchors. Socket bolts and various nuts are stocked with many types of washer and sealing washers. The stock lines here at Challenge Europe of course include numerous other industry standard fasteners and ancillary components.
Naturally, where there are standards customers also look for custom specials, and we are capable in this area too, working with thread forms and materials to suit the individual application.
Once specified and sourced customers can take advantage of the many service packages available from stock-holding-and-control to production-system-integration such as Kanban, Lineside Supply or Vendor Managed Inventory (VMI).
Contact us to discuss your specification or production needs.