Which is the correct side of the copper washer?

[Fernando Mendes]

The flat side of the copper washer is toward the screwhead or.....

[Plymouthy Adams]

what copper washer are you referring to?   sound as it is not just a standard flat washer or standard application.....a standard flat copper washer (common to brake banjos etc) has the same properties each side...your question point to something altogether different and of special intent.

[Fernando Mendes]

It has a round and a flat side.

[ggdad1951]

Looks like a stamp formed washer so you have slight roll in on one edge and sharp on the other.  Personally, I put the round edge against the larger flat surface and the sharp edge by the bolt head, as any deformation of the parent material in the stamping process will create a SLIGHT concavity/convexity.

[lostviking]

Not to just be contrary, but I always put the rounded side towards the head of the bolt. The bolt has less surface to be making contact. The flat thing you are putting the washer against has the larger area. That is just my thinking, I've not read anything specific either way.

[ggdad1951]

its a crush fitting so likely doens't REALLY matter. 

[lostviking]

Completely agree in this case. I am just a creature of habit, and that's how I've always installed washers...and why I make that choice.

[TravisL17]

This thread made me think of this picture I saw a while back. Makes me laugh as I also have a preference on washer direction. It likely doesn't matter much, it's more of a habit and being particular.