I can't find mine atm, but it's basically an 'I' shape.
The top of the I is the handle and the bottom of the I goes in the 'cutouts' on the caliper piston, twist and push, don't forget to unscrew the bleed nipple first ;)
I built one myself using MDF, no problems so far. I doesn't get daily use though.
I've also changed it a little.
1) I got a proper (cheap) sandblasting kit from a kit-car show to replace the spot blasting bit.
2) I don't use the failed blue vortex tub, never worked well enough, just use a...
I agree with the above that it needs to have both sides on, adds rigidity.
This is a simple one we put together for putting bearings on an Escort axle. Works for bushes too, I have a selection of sockets that fit most things. Locost thinking.