There are several individual PPI designs which each have their own specification. These specifications have to be followed when producing artwork for mail pieces.
Your PPI licence number must be added to the PPI see example below.

The HQ
number is unique to Uni Mail. Other mailing companies or organizations with Royal Mail accounts will have their own HQ numbers. The various different PPI designs can be downloaded from the Royal Mail website ready to be used.
When reproducing PPI’s the Royal Mail prefer the user to keep them to maximum and minimum sizes:-
Square PPI design 1:
Rectangle (large) PPI design 2:
Rectangle (medium) PPI design 2:
Rectangle (small) PPI design 2:
More information regarding PPI’s can be found on the Royal Mail website www.Royalmail.com