Anti-tamper Seal, Image & Found by TerraEnglandia.
Found in North Yorkshire, 20mm.
Faint inscription & markings on both sides
From finder, "On one side, I think I can see the letters BASI, I think it may just be partial text though. There may be some sort of design below the text."
From Steve_JT, "another possibility is a seal off an engine diesel pump from a tractor or other machine. They were used to stop people tampering with the diesel delivery to the the engine or governors, that could increase the power of the tractor".