On Thursday, 24 January 2019 07:53:28 UTC, Andy Burns wrote:
polygonum_on_google wrote:

they were not butted, not mitred, but had some routed edges. The
shape meant that the corners meshed into each other and made very
neat, straight lines.
corner lock mitre?

https://www.axminster.co.uk/axcaliber-mitre-lock-cutter-ax805970

Spot on - many thanks. Had wandered round Axminster site and not found that.