Why does this mounting hole have this shape?

I have a Fein "Multimaster". It's an electric hand tool with various
"blades". For sawing, sanding, cutting. It works by vibrating very
fast & with very small displacement.
The various blades have this mounting hole:
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The "points" on the hole do not engage anything on the tool - the blade
is free to be rotated to any position & then fixed in place by
tightening a screw. I.e., it's fixed by friction.
Why, then, does the hole have those points?
Reply to
Bob Engelhardt
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Winston & Dave replies got me to take another look and I found nice sharp edges in the inside points. But the clamping washer is domed and only presses beyond the outside points. Hmmm?
Then Ned & Mike nailed with "other model compatibility". The new models do have star-shaped mount. Now I'm wondering if I need the adapter for my old model (I didn't know it was an old model!).
Thanks to all, Bob
Reply to
Bob Engelhardt

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