There’s a 20 thousandths piece of sandpaper (~120 grit, both sides) between the 2 parts.
Hose or pipe attachment? You put screws through the slits, which are wide to give you some room to adjust the placement sideways.
What does the other side of the plate look like?
Is it aluminum-zinc alloy?
What diameter tube will fit under the knob?
Sandpaper was likely added by a user to lock the angle.
What is the angle on that bevel?
It reminds me of a tool rest attachment from a lathe.
I’m with DaveR, What diameter tube is it designed to fit? 1/2” or 1”?
Could be a “flag” holder for film lighting. Designed to hold a bounce or blocking card on a tube armature. Usually made of cast aluminum, but this does look perhaps a bit too robust
I could see lathe tool rest, does the other side have a groove in the face?
It’s cast aluminum, surfaced flat on the bottom, the tube diameter would be 1" and the bevel is 40°, and the hardware is 3/8.
Or a bench grinder. But what are the slots for, if it is either of those?
I tried googling the part number, but no joy.
Probably to fix it to a machine bed or to attach some sort of removable fence. The bevel is there for a good reason. Some planer fences have that bevel to allow rotation, but it doesn’t seem orientated right for that. It could be for a sliding ripsaw fence but I can’t decide how it would be orientated.
Because of how adjustable it is it’s making me think its for a machine of some sort either to hold a tool or guide a workpiece.
I could be wrong of course!
looks like some type of honing guide.
Found it! It is the table from a Craftsman Drill Press (Model 33.25926):
I don’t remember ever having/using one of those but there is no doubt in my mind.
My father had a similar one. An electric hand held drill clamped in under the bail. Not a great substitute for a drill press but if you couldn’t afford a real drill press…
It would really be something if I found the rest of it in another junk box.
Looks like all you need is the hand held drill.
Looks like a schyspangyl.
Which Harry Potter?