Why not simply use the term 'decade'? It's fairly common in the engineering field, and in this contex probably means something like groups (or rows) of ten, as Kate suggests.

Sentences before the mentioned one:

This seems to be part of the marking system for the products which seems to have something which is 'in six groups of ten' and where the letter height is 7mm I don't know if that makes any sense in the context (I'm thinking of something like a bar code

Mijn excuses

Can you give us some more context perhaps? Which particular area of engineering for instance? Is it publishing?