Is there a documented definition of Tier I vs. Tier II suppliers?

[Sam]

I thought I posted this question once before, but I can't find; so here goes again.

Is there a documented definition of "tier I/Tier II" suppliers?
I "assumed" a Tier I supplier was one that supplied directly to the OEM and a tier II supplies to a tier I. However, I have been asked to provide evidence to "prove" my asumption,but I can't find it in any of the related documents.

 

[matthew evans - 2002]

WE ARE A SUPPLIER DIRECT TO FORDS. WE ARE DESIGNATED AS A TIER 1 SUPPLIER. TO MY KNOWLEDGE WE HAVE NEVER BEEN ISSUED WITH A DEFINATIVE DESCRIPTION OF THE DIFFERENCES BETWEEN TIERS BUT YOUR DEFINITION IS CORRECT AS I UNDERSTAND IT.