I found these on a recent 10 min sweep through the old WW2 Airfield area @ approx 5" depth.
Before i start to unnecessarily clean it all up... any clean examples around? Any ideas?
My thoughts are, 4x4 vehicle oil or water cap! It still has its rubber seal.
Here is what I can read under the hardened dirt:
MADE IN ENGLAND
PATENTED IN VARIOUS COUNTRIES
There is more but under the muck.