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We are always happy to provide practical solutions to your fastener and turned components enquiries. Your questions are often the source of some very interesting FAQs and we've compiled details of some of the most commonly asked questions. If you can't find the answer you are looking for below, please email the team at and they will endeavour to answer your query.



Types Of Spring Pins: Slotted & Coiled

Coiled pins and slotted pins are types of mechanical fastener that provide a versatile and cost effective fastening solution.

Slotted spring pins are rolled from stainless steel A2 or spring steel into a hollow ‘C’ shape. This type of fastener has a slot running down it’s length, which is sufficiently wide enough to enable the pin to contract as it is driven into the hole. After insertion, the force of the pin against the wall of the hole will keep the pin secured. Technifast offer a choice of heavy or light duty pins depending on the application.

A coiled spring pin is a hollow cylindrical pin, formed from a 2¼ coil of either spring steel or stainless steel with swaged chamfers at each end to aid insertion. The coiled pin is a self-retaining fastener which works in a similar manner to a slotted pin, but the design allows for the stresses to distribute equally across the coils after insertion. To provide for different requirements of strength and flexibility Technifast stock a standard duty recommended for most applications and a heavy duty version which is typically used in high shear strength applications and hardened host materials.

Installation of these types of pins requires very little preparation, the user simply needs to drill a hole of an appropriate size to accommodate the pin; there is no reaming operation involved which, in turn, helps to keep production costs low.


What Are The Benefits Of Zinc Plating?

Zinc plating is an established process suited to hardened steel base materials. It offers added protection to steel components against corrosion. The zinc creates a barrier acting as a thin, sacrificial coating, helping to prevent corrosion from reaching the steel surface of the component beneath.

Zinc is a widely available material and depending on the application and quantity, it can be a cost-effective option for businesses on a budget when used as an alternative to stainless steel. 

Stainless steel is generally more expensive than a zinc plated option, due to the chromium content of stainless steel. However, the benefits of a cheaper alternative would need to be considered against the strength and corrosion resistance of stainless steel.

Aesthetically, zinc plating produces a bright finish and superior appearance to an uncoated steel component - which is an important factor if the fastener is going to be visible within the intended application.

Technifast work with respected and established plating and finishing partners to provide a high-quality service, which we offer as part of our manufacturing service.  We do not offer these services on parts that have not been manufactured or supplied by Technifast.


Should I Choose A2 Or A4 Stainless Steel Material?

The grade of stainless steel used for a component will be determined by the environment the fastener will be exposed to.  Selecting the correct grade of stainless steel ensures the fasteners will be of a high-quality and perform in the application for which they are intended:

A2 Stainless Steel is a commonly used grade, as it’s very versatile and offers strong abrasion resistance, plus a good resistance to corrosion and high-hardness levels.  A2 stainless steel is from the austenitic family, containing 18% chromium and 8% nickel. 

A4 Stainless Steel is the best option when the component is to be used in a harsher environment.  The addition of molybdenum to its composition provides the A4 grade with a greater level of corrosion resistance, making it suited for use in salt water or certain chemical solutions.  Many fasteners used in the medical industry are manufactured from A4 stainless steel.

Stainless Steel A2 is typically a lower-cost option, but the additional cost of stainless steel A4 is a good investment, due to the fact it is very resistant to tarnishing and corrosion, making it a long-lasting material to use.

What Are DIN And ISO Standards?

DIN is the acronym for ‘Deutsches Institut für Normung’, which is the ‘German institute for standardisation’ who developed detailed technical standards for the engineering industry, amongst many other industries.  With reference to fasteners, DIN number indicates the that the part conforms to a specific metric standard.

The International Standards Organisation (ISO) standard has evolved to supersede the DIN standard, which was historically the predominant metric fastener system referred to.  The intention of the ISO standard was to standardise the technical specifications worldwide to simplify the system and aid the flow of trade via a universally recognised standard.

In practice, DIN and ISO standards are still both commonly used when specifying fasteners and both standards are recognised by Technifast when our customers specify the fasteners they require.

What Are The Differences Between Interference / Transition / Clearance Fits?

Engineering fits are defined by the allowance of tightness between two mating parts - usually a shaft and a hole - of an assembly.  The type of fit used is identified by the relative movement required between the components to allow the parts to perform their specific function.

Clearance Fit: If the assembly requires the components to move freely in relation to each other, this is termed as a clearance fit.  In this type of engineering fit, the maximum permitted shaft diameter is less than the diameter of the hole.  When using this type of fit, the clearance value is always a positive number. 

Interference Fit: With an interference fit, the components of the assembly mate together tightly, so that relative movement is not possible.  The minimum diameter allowance of the pin is always greater than the maximum diameter of the hole, meaning an interference fit is mainly used as a permanent assembly for parts which rely on rigidity and alignment. 

Transition Fit: A transition fit sits between a clearance and interference fit and can have a positive or negative clearance between the mating parts. This fit is used when an accurate location is required, but a small amount of either clearance is acceptable.

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