What is this? It came with a HF mini lathe that I just bought and I have no clue what its used for... anybody know?

[dml66]

I bought one like that to mill a flat into a piece of 5/16" mild steel using my 7x10 mini-lathe, I got it done but it was tedious and nerve-wracking, it's now a shelf ornament.

 

[GrifterGuru]

I bought one like that to mill a flat into a piece of 5/16" mild steel using my 7x10 mini-lathe, I got it done but it was tedious and nerve-wracking, it's now a shelf ornament.

Yup, they do tend to spend more time "stored" than in use, though I have used mine fairly often.