M4 X 50 Hex Head Set Screw 8.8 DIN933 BZP

These 8.8 tensile hexagon head set screws DIN 933 are full thread where-as hexagon bolts DIN 931 are part thread and the remainder of a bolt is a smooth shank in-between the bottom of the hexagon head and the beginning of the thread.  The length of the shank and the thread vary to a formular depending on the size of the bolt. Tightening strength and torque is worth checking for critical applications to prevent movement of the material under certain stress conditions.

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.  These are usually stamped on the head of the set screw or bolt.  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.

These are bright zinc plated fasteners which is a preventative measure from corrosion.  Avoid breaking into the bright zinc plating usually abbreviated as Bzp as this will cause faster corrosion if not covered with a corrosive protected material as in time this will weaken the fastener.  Also bear in mind using different materials can cause fusing through corrosion especially in damp conditions when mixed with aluminium or stainless steel materials.

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.