This is a block and tackle pulley system for use with 5mm paracord (I am sure other sizes could work too)
It requires two M5 carriage bolts >35mm, two m5 nuts and two small washers to fit between the nut and the printed block.
A large washer inside between the two pulley wheels may also be necessary.

Print 2x: Block 13042018
print 4x: Pulley wheel

pulley wheel 13042018 creates an 11mm wide pulley wheel If using pulley wheel 13042018 then there is no need to include the large washer. (not recommended)
pulley wheel 20042018 creates a 10mm wide pulley wheel if using pulley wheel 20042018 then a large washer (30mm diameter) is necessary. (recommended)

I intend to improve the design at some point in the future by reducing the friction created by the faces of the wheels and possibly adding bearings.