STAINLESS STEEL FLAT & MUDGUARD WASHERS METRIC

Flat Washers (Standard)
Standard flat washers are primarily used to distribute the load of a fastener over a larger surface area to prevent damage to the material being fastened. They typically have a smaller outer diameter compared to mudguard washers. 

Mudguard Washers (Large Diameter)
Mudguard washers, also known as fender or penny washers, feature a significantly larger outer diameter than standard flat washers to provide maximum load distribution and prevent pull-through, making them ideal for use with soft or thin materials, or oversized holes.

The primary difference between 304 and 316 stainless steel is the addition of molybdenum in grade 316, which significantly enhances its resistance to corrosion, particularly from chlorides and saltwater environments. 

Chemical Composition
The key distinction in composition is the presence of molybdenum in grade 316, which is absent in grade 304. 
Grade 304: Contains approximately 18-20% chromium and 8-10.5% nickel. It is often referred to as "18/8" stainless steel.
Grade 316: Contains lower chromium (around 16-18%) and higher nickel content (10-14%), plus 2-3% molybdenum. 

Explanation of Dimensions (M5 X 10 X 1.0)
Here is a breakdown of what each part of the designation signifies:
M5 (Inside Diameter/For Bolt Size)
The "M5" (Metric 5mm) indicates that the washer is designed to be used with an M5 bolt or screw.
The actual inside diameter (ID) of the washer's hole is slightly larger than 5mm (typically around 5.3mm) to allow it to fit over the bolt or through the hole easily.
10 (Outside Diameter)
The "10" indicates the outside diameter (OD) of the washer is 10mm. This dimension determines the surface area over which the fastener's load is distributed.
1.0 (Thickness)
The "1.0" indicates the thickness of the washer is 1.0mm. The thickness contributes to the structural integrity of the joint and helps prevent the bolt head from digging into the material being fastened.