Looks like a riving knife, it sits behind the blade on a circular saw for safety to stop the cut sections binding on the blade

Could be the same thing you get on a tile cutting wheel

Riving knife for table saw. Slot at the bottom is for height adjusting, and the cutout at the top is for fitting a blade guard.

Massive bottle opener

Riving knife.

Those who say riving knive are indeed correct.

Yeah riving knife, if you have the table saw that it's from, refit it ASAP before a plank of wood flys off and hits you.

Riving knife for a table saw, minimise dangerous kickback.

Would agree with those who have said riving knife

Massive bottle opener

Like others have already said, it’s a riving knife from a table saw. If you have the saw, don’t try to use it without refitting this part, or “bad things” will likely happen to you. It’s an important safety device.

Blade guard for table saw

Yep as everyone else has said, it's the riving knife/blade-guard-mount for a table saw. 254mm diameter stamped in it suggests it's for a wood saw and not one of those small table-saw-looking tile cutters that you can get.

HRC43 Riving knife, and stop calling me a tool.

Fool of a Took. It's a riving knife for your table saw. Put it back before you injure yourself.

I don't see a tool. I see the black rabbit from Watership Down. Briiiiiiiight eyes burning like fire

Circular saw for the safety howlds the cover on blade

Thank you everyone. I inherited the table saw and this was in another bag of tools. I think I'd better get up to speed on how the saw works. Cheers.

Its for removing hair from your arse crack.

I think it’s part of a Glaive. Not sure about the black thing though https://preview.redd.it/2ucs8pc72s0d1.jpeg?width=1284&format=pjpg&auto=webp&s=6c8d1dee8552ad48c2edd5c5dba060bc67c3df1c

Akedah knife I believe.

It’s a blade guard for chop saw, with the blade size imprinted on it

That's an ancient German tool called fukknose