I’m not sure that’s a cassette.
It looks to me like you’ve made yourself a freewheel puller. Freewheels tighten by pedalling action and can be on wickedly tight.
A very common method is to stick the tool in a vise solidly mounted to a bench solidly anchored to a wall, put the wheel on top, grasp it like a bus steering wheel, then ”turn left”.
If it is a cassette, you’re about to open the part that holds the DS wheel bearing cup and the coasting mechanism.
On Shimano Uni-Glide - which is somewhat similar to yours - that is a reverse thread.
Determine what you have before trying harder.
I’ve made DIY freewheel pullers on occasion. Never managed to get one made out of ”household” grade steel to work. Have had some luck starting with an appropriately sized tool socket, then grinding away material to form the tabs.
I appreciate the attempt though.😁👍