Technical Area


Definition of Stainless Steels

The Stainless Steels are alloys iron, chrome and carbon based, enriched with other elements such as nickel, molybdenum, silicon, titanium and more.

Their main characteristic is the high resi stance to the corrosion of the atmosphere.

This characteristic is due to the spontaneous formation of a thin layer of chrome oxides (Pict.1) that protects the metal against the corrosive attacks.

Designation of stainless steel fasteners

Extracted from UNI EN ISO 3506

The designation system of the Stainless Steel quality and Torque Value of the screws and cage screws is given in (picture 1). The designation of the material consists of two blocks separated by an hyphen. The first block shows the Steel quality, the second the class of resistance.

The designation of Steel quality (first block) consist of one letter

A Stands for Austenitic Steel

C Stands for Marstenitic Steel

F Stands for Ferritic Steel

Prescriptions for the selection of stainless steels

The main characteristic of Stainless Steels is the high resistance to corrosion, different depending on the different materials that make up the inox world.

Nevertheless there are important characteristic that guide the selection of the material, such as:

– mechanical resistance

– surface hardness

– workability to machine tools

– deformability (forming attitude)

– availability

Stainless steel families

We can distinguish three families of Stainless Steels basically:

a. Martenistic can be hardened with a heat treatment

b. Ferritic, a stable structure, despite the temperature

c. Austenitic a stable structure, despite the temperature

During these last years two new families have made their appearance, whose use in the fasteners field is quite small for the time being:

d. Duplex Stainless Steel

e. Super-Austenitic Stainless Steel

Tightening momentum for stainless steel fasteners

In a link made out of screws, the strength the screw keeps all the parts together with, is called pre-loading.

As long as the static /and/or dynamic stress are below the bolt pre-loading, the screw will not unloose, granting the link to be fully functional.

On the other side, the bolt pre-loading will not have to be higher than the toughness of the screw, if so it would cause the breaking of the screw itself.

As a result it’s very important to define, taking into consideration other parameters too, the maximum pre loading to be applied on the screws, more precisely the maximum value of the elasticity (over which the screw buckles permanently).

The pre-loading can be indicated also through another value which is the tightening momentum.

When mounting, please be careful

When mounting screws and bolts you have to bear in mind some precautions:

• Choose only the screws and bolts belonging to the nobler degree of the galvanic scale. A totally cathode material in its mass is a higher guarantee than a less noble, simply protected on the surface (zinc plating or coating).

• Avoid junctions between different metals when there is an electrolyte. In case it’s not possible, avoid direct contact between the two parts with the interposition of isolating gasket.

• Make sure that the less noble material doesn’t have a smaller surface in comparison with the nobler. The first, in fact, would corrode, sacrificing itself towards the second one. Given the small dimensions of the fixing elements such as screws, nuts, washers compared with the joining elements, this aspect turn out to be of vital importance.

Alloy Surcharges

We thereby report the extra-league values of wires and wire rods as regards the AISI 303/304 and AISI 316 belonging to the last months:

di trafilati e vergella per AISI 303/304 e AISI 316 degli ultimi mesi

extra-league values of wires and wire rods as regards the AISI 303/304 and AISI 316

Seizure phenomenon when mounting stainless steel fasteners

When mounting stainless steel nuts on screws or threaded parts it’s likely to run into the seizure phenomenon of the nut on the male thread.

The attachment describes the phenomenon and clarify the aspects affecting it.

See the phenomenon

Passivation of stainless steels

Pickling and Passivation becomes of primary importance when we talk about an Inox Component. In fact they put this material in the best possible conditions for promoting the passivation mechanism, this last being at the very base of the stainless behavior.

Reed the article

Stainless steel in fasteners comparison table

Below please find a link to the download of the comparison Table for the most common Stainless steel used to produce fasteners.

See the table



Professionalism means recognizing the need of a customer and knowing how to fulfill it. For Fiminox, guaranteed quality compare to deadlines and great reliability in commercializing INOX screws and bolts, are pillars of daily activity, as well as the main strength.


The high quality service offered comes from the experience gained in the field of stainless steel fasteners both in the unified market and in the production of special parts.


A high technological level is essential in order to guarantee certified products in compliance with the regulations in force. Since 2003 Fiminox has relied on a company quality system certified by DET NORSKE VERITAS (ACCREDIA accredited body) and recently updated according to ISO 9001: 2015 procedures; this guarantees our products according to the criteria of total quality with the control of technology and of the entire production process. The incoming controls are carried out with the most modern equipment that tests dimensional accuracy, functional and chemical correctness. The same attention is given to the checking out materials that are carried out through optical readers and bar codes and are based on a double level of verification.


Implementation requirements for pushing more and more industry to the use of special, and a specially developed and designed.

Experience, flexibility, and the taste for novelty

Fiminox Tekinox

make a reliable and competent in the field of special fasteners also printed and small machined parts.


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