Numbers on front wing

[Ken]

Working on the off side front wing today (2a suffix d ) I was surprised to notice the number 88 stamped on the engine side of the inner wing low and at the rear.
I can't find the same on the near side wing.
Presumably it refers to the wheel base, but why on one only and does this mean that the 109 had different front wings. Or does the number mean something else?

[nathanglasgow]

The 109 has different inner wings. I have got 88 stamped in my 88" wing also.

[Old Hywel]

Deeper chassis on 109, smaller gap to fill.