"that is to say" is fine. You could also use, "that is" or "in other words".

I agree with Svaihingen, and you: 'thus' doesn't really work here.

i.e. might be possible, too. Deckscheibenkopf and Außenringeinstich don't sound remotely the same to me, but apparently they are, or at least that's what the 'also' implies.

I agree with Gibson on i.e., but to describe what this is about i'd say seen axially the position of the Deckscheibenkopf and the Außenringeinstich are the same. From this position starts the dimensioning of the Deckscheibenfuß.
... I hope you have a drawing on which you can identify those three parts :-}
Außenringeinstich is probably an outer circular incut? ...

"i.e." or maybe "in other words: xyz" sound fine for me.

(I won't comment on the Deckscheibenfuss and the Aussenthingy - I sure hope there are some drawings accompanying the description)

Thank you all! (Yes, there are drawings. ;-})