M4 Full Nut DIN 934 A2-304 Stainless Steel

These are stainless steel A2-70 hexagon full nuts DIN 934 which are ideal when a nut needs to freely be used to secure bolts or studs.  To share the load it is recommended that a stainless steel A2 flat washer is used.  To prevent the full nut to come undone due to elements of vibration or movement a locking washer is also needed such as a spring or serrated washer again in A2 Stainless Steel.

It is important to get the correct tensile strength for the application its being used for as either a higher tensile strength or lower tensile strength may be suitable. A typical stainless steel A2-70 fastener has a tensile strength of 700 MPa (mega pascals). Ideally a matching tensile strength of nut to match the tensile strength of the bolt or stud needs to be applied.  Having a higher tensile strength may not always be suitable on certain applications as movement and stretching of the materials being joined together or the breaking point could be important so always check suitability for specific applications.  Once the fastener has been disassembled it’s advisable to replace all components such as the fastener nuts and washers together with the set screws or bolts.  The reason is that the fastener over time will experience stretching of the threads of when it was tightened up plus the likely constant movement may cause fractures causing weakness to the fastener. Tightening strength and torque is worth checking for critical applications to prevent movement of the material under certain stress conditions.

Stainless steel fasteners provide prevention to corrosion if not mixed with other metals.  They are suitable in conditions where its likely to get damp such as outdoors or when in contact with water.  These are typically used in food industries or other outdoor applications, but they are not suitable in a salty environment such as at sea.

More information is available from Central Fasteners regarding fastener details, but its always worth checking with a manufacturer's specifications or drawings if an alternative size, tensile strength or types of nuts and washers are used.