High quality ratchet handle with 10mm (M10) female thread.
Of course it is not a ratchet but a type of spring loaded clutch. You pull back the lever to release the clutch and position the handle to get it out of the way when tight.
This is nicely made and very strong. Much better than the typical handle you find on Far-Eastern made lathes. The large diameter glass fibre reinforced nylon ratchet and handle will give years of good service.