HF sandblaster

[Cuda416]

What's the small brass fitting in the bottom pipe for?

If you're referring to the small ball valve, it's to let air in. The metering valve works like a spray gun/carb etc. The air rushing by pulls the media with it. It can be adjusted to "hopefully" maximize the effect.

 

[Bodyperson]

Bag says coal slag, and its black. Not sure what it is, but it works!

Okay. Standing corrected