yeah, I had a subaru with em. that design is all over the place.
Pic my tool kit, our son found this in a batch of auction stuff he bought. He did not need it and gave it to me.
I have had two cars with rear discs in my herd for years. First '91 Lin Cont, and '95 Sable wagon. I have to replace rear rotors about every 2 years due to rust, and I do this myself. I have a home made tool for Ford but now I have a pro tool it is off to the scrap box.
Pic of a caliper off my '03 wagon, boot was rotted off and I replaced with rebuild calipers. I used the old one to practice using my new tool. Very important: you cannot turn the piston if any force is applied to the tool. The hex part on the threads are for pushing front calipers in, not for using beyond hand tight to keep the pins engaged in the piston. Any force on the piston and it will not turn. Added to that, and any caliper, the bleeder should be open to allow pushing in without forcing dirty fluid back up the line. My Buick, I did not use the bracket, only pushed the tool in by free hand and it turned the pistons in with ease.
My tool looks to have been used hard and abused as the Tee handle is bent. Someone used a cheater on that. It is designed for hand use only. If it takes more, you are using it wrong, or the piston is frozen.
Tip: when turning the piston in, when it reaches bottom it can be turned further to align the slots to match the pad pins.