This question already has an answer here:
basically I'm looking to press a single keyboard shortcut, similar to Cmd+Shift+4, except rather than having to draw my own box, I'd like a box of a predefined dimension appear, such as 300px x 300px that I can move around.
Or an alternative would be to have Cmd+Shift+4 work at a fixed aspect ratio, for example hold down alt and it will be locked to 1:1
The only tool I've found to do this is Snapz X Pro but the price is a bit crazy when I only need it for make screen snips.
My job has a task that requires making multiple (dozens or hundreds) of 1:1 screenshots of various things, I can't fiddle with the mouse down to the pixel. I also can't deal with going through 3 menus and saving and typing my own file name either, but that wouldn't be the end of the world.
If I could just lock the aspect ratio with Cmd+Shift+4 I could start large and batch resize the snips when I'm done, that would be a good alternative.