This is an adapter for a reciprocating saw to allow shaking of spray cans.
Slide it over an old saw blade and make sure the adapter doesn't touch the saw's front end when the blade is reciprocating.
Then drill a 3.2 - 3.5mm hole through the blade at the hole of the adapter and fix the adapter on the blade with a M3 screw and nut.
To make sure the can is not wobbling back and fourth while shaking, put e.g. some self adhesive rubber feet or any other sticky material inside the adapter's walls where the spray can sits.
To secure the spray can onto the adapter, I used Velcro tape cable wrap.

You can get it here for example:
https://guide.alibaba.com/shop/yellow-yard-roll-velcro-cable-fastening-tape-0-39-inch-velcro-cable-ties-organizers-one-wrap-hook-and-loop_57636646.html

The Velcro tape will hold itself onto the adapter when wrapped around through the small slot on the bottom of the adapter.
It's also possible, to put the screw fixing the adapter to the blade is punched through the Velcro tape. Make sure to use big washers so the tape doesn't slip over the screw.

I found it works best when the can is hold vertically upwards or downwards to allow the steel balls in the can bouncing against the bottom/top of the can.
Holding the can horizontally while shaking keeps the steel balls in the middle of the can without much effect.

Have fun.