Spring washers are locking washers that are used when there is a need to prevent a fastener from loosening as a result of vibration. They are also often called split lock or split ring washers.
A spring washer has a split in the washer section that when tightened each side of the split bites into the nut and the mounting surface. This “bite” prevents any anti-clockwise rotation from occurring under vibration.
The term “square section” refers to the end section of the split in the spring washer.
An imperial washer can be used in conjunction with all types of non-metric threads including UNC, UNF, BSW, BSF, BA etc.
Steel products described as having a self colour finish are best suited to internal applications, as they have no additional protection against corrosion. The shade of a self colour finish can vary from bright metal to black, and it will change over time with oxidisation.
If you plan to use self colour finishes outdoors you should paint them to give them a protective coating.