Found this metallic(?) disc submerged in a little stream in the italian alps. It's about 10cm in diameter and 2cm thick. I didn't take it out, in case it's some kind of explosive (which I doubt).

What is this remote control type of thing? Keychain sized, needs 2 AAA batteries. May possibly emit noise?

Some kind of metal cap on the ground outside a prewar NYC apartment building

What is this thing? 5" rusty metal tool with grip and a wrench, found in western North Carolina

Eastman Kodak Co. solid aluminum (?) block with dial and measurements

The two threaded holes are the only thing other than the dial on the cube. I image this is part of a camera setup, maybe mounted on a tripod to get precise image adjustment for the camera? The dial has very small threads and takes quite a white to spin. There are other measurements on the shaft that the dial is mounted on, I think 1-10?

What is this tank next to our hot water heater?

It is very loud, is it safe to put a towel over it to reduce the rattling noise?

What is this horizontal piston-like thing connecting the body of two passenger train carriages with each other / with the bogey?

Weird black and white sand substance around our furnace in our basement

4 inch metal bolt with a spinning wheel around the head. "TG" is written on the top.

Wooden handle metal loop, plugs into wall, stamped with “pioneer electric 500watt 120volt model 622”

What is this marble marker in the sidewalk in Burlington, Vermont?

I found two of these markers in the sidewalk along South Willard Street and then one in the second block of Howard Street? Are these historic property markers or do they have some other significance?