Why there are two colors in the same batch of products?
Note, there are different batch numbers!!!
Certain materials' features cannot always be guaranteed to be exactly alike in production.
You can explain to the customer that the visual appearance of nuts surfaces is dependent upon the colour and coating.
We cannot guarantee that a certain color will always have the same shade.
The colour formed when stainless steel is heated, is dependent on several factors that are related to the oxidation resistance of the steel.
The heat tint or temper colour formed is caused by the progressive thickening of the surface oxide layer and so, as temperature is increased, the colours change.
However, there are several factors that affect the degree of colour change
The colours formed can only be used as an indication of the temperature to which the steel has been heated.
to prevent galling (lock nuts can generate friction and heat during installation, which cause the nut and bold to tighten while it’s not completely installed)
In your case, the first batch number has a natural color look.
The second batch of 226 pieces has an extra protection against galling which makes the nuts look shiny white silver look.
It’s only recently that the stainless steel nuts are now having also this feature.
You should explain to your customer that the natural color nuts are 100% performance and corrosion resistant as the ‘silver’ looking ones.