It looks to have been in sand laden soil conditions going by the underside. That 5mm would have eventually turned to 0 if given enough time. I've seen a 1970s thumb latch base with slits of missing aluminium carved through!!

It's a shame about the scraping. I can never understand that. Weed wackers put paid to the need to get close to walls.

Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!