Fasteners for assemblies with relaxed tolerances

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This article explores the benefits of using fasteners that can compensate for vertical and horizontal misalignment in assemblies where cost is more important than tight tolerances.

Fasteners for assemblies with relaxed tolerancesWhile design and production engineering for some applications requires fastening to occur with tolerances measured in microns – medical equipment and electronics assemblies, together with aerospace and defence products, being good examples – it is a fact that, in the wider manufacturing arena, there has to be, by necessity, more latitude. In simple terms, manufacturers of helicopters will have a different view about what assembly tolerances are necessary and acceptable to those that manufacturers of hairdryers may have! Money talks and, in the manufacturing environment, few OEMs will see the need to spend any more than is absolutely necessary to achieve an ‘acceptable fit’ during an assembly process.

Whereas no-one would suggest that lack of precision is deliberately designed in, manufacturing practices and tolerances in non-critical applications must nevertheless be suitably accounted for at the design stage. For OEMs keen to remain ‘in profit’, a lean towards a more justifiable ‘close enough’ assembly fit can be appealing, if it is more cost efficient. With the presence of a wide variety of unavoidable contributory factors affecting tolerances in the materials, manufacturing and assembly of many products, some OEMs have reached the conclusion that a fastener which could compensate for these variations would prove very useful and a much more cost-efficient approach than amending upstream processes, practices and materials choices.

Recognising this, the research and development team at Bollhoff Fastenings used feedback from its field engineers and application experts across many of the industries the company already serves, in order to design, test and ultimately bring to market an innovative tolerance compensating product. Launched in 2002, Flexitol was introduced specifically to provide design and production teams with a special fastener for use where a certain degree of misalignment could be expected during assembly operations on the shop floor. Use of the new fastener is said to have transformed previously challenging (and sometimes costly) misalignment issues and turned this stage of manufacture into a routine process unworthy of further comment, aside from better throughput and the ongoing cost savings obtained.

Key applications

Bollhoff cites a number of key applications in the automotive industry, covering passenger cars, utility vehicles and trucks, where Flexitol is already widely used. Included amongst these is the assembly of headlamp units, mudflaps, cab linings, instrument panels and rear lights. Some automotive OEMs also use the product for roof rail mounting. Applications outside of the automotive environment have seen Flexitol specified in the assembly of frameworks, roof ledges, washing machines and electric drive units, to mention just four. Other advantages highlighted include the fact that the fastener is a ‘blind’ item, so installation only requires access from a single side. Additionally, Flexitol fasteners can be inserted either manually, for low-volume production environments, or by fully automated systems that might form part of a high-volume production line.

Flexitol tolerance compensating fasteners can be used to overcome misalignment in both vertical and horizontal planes, and offer guaranteed repeatability in both axes. Interestingly, the portfolio also includes products catering for misalignment in banjo fittings, too.

Bollhoff’s UK Industry Sales Manager Clive Brown says: “One of the real keys behind the success of Flexitol is that the range is so extensive, with a variety of designs available for different applications, plus the fact that we can design a bespoke solution using the established principles, should a customer require it. The fastener is also available manufactured in a variety of materials, including metals, alloys and plastics, as well as metal/plastic hybrids. This wide choice makes Flexitol compatible with so many uses, and some products in the Flexitol range can cope with misalignments of up to 10mm.”

To learn more about the Flexitol range please visit

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