I assume by flat spot you mean the top of the bar where it fits into the handle.
these are to ensure that the cutting tip is level or pointing just a tad downward from level.
as long as the back rests are level on both machines you can move the tools from one to the another.
I've used my Jamieson set up on a jet 1642, Powermatics, Oneway 2436, 1018 & 1224, Stubby and maybe a few more.
happy turning,
Al