This is a pinch block intended for pinch grip training.

To complete the tool, thread two ends of a rope (e.g. paracord works well) through the separate holes from the bottom, tying knots on top. You may want to tie multiple knots or use a washer to make them thicker. Then attach a carabiner with weights to the rope and lift.

To use the tool, pinch the opposing walls between your thumb and the other 4 fingers, then lift the weight vertically. Do not rotate the tool, don't let your fingers grab under the bottom edges of the tool - then you'll no longer be training your pinch grip!

This Thing includes an STL for a thicker tool (40mm x 160mm x 90mm) as well as a narrower tool (20mm x 100mm x 50mm), but you can also use OpenSCAD to fully customize it.