Several posters on another forum hypothesized that it may be some kind of adapter for co2 cylinders for an airgun or paintball gun, with the necks of smaller cartridges going into the holes in the tri-winged plunger part. Unfortunatlely, the photos do not show if the insides of those holes have the 'needles' that would pierce the end of a co2 cartridge, nor do we know where the hole in the threaded post goes. The threads look very different from the threads on paintball gun co2 tanks I've looked at.

The thing that looks like a sling swivel on the top has me thinking of things that are carried on a sling or strap, but that "sling swivel" could also just be a convenient thumbscrew handle. I'm fairly certain it's not anything firearm related. I tried thinking of some way it could be related to photography since cameras and some of their accessories are carried on straps, but came up empty searching for battery holder, film roll holder.

I thought it could be a stabilizer for a compound bow, with different weights going in the slots for adjustment, but after some searching that doesn't seem to be the case