Summary

Just in case you want to rotate something using your hand, you could use this hand grip with bearings ...

I am using a M5 rod. But you should be able to use another size up to M8 by changing the scad files.

To build a crank you will need 2 additional shaft couplings and 2 more threaded rods. But now it is about the hand grip.

Well, ball bearings are overkill? Just set the size of your favorite big washer in stead of the bearing's size in the Openscad file.

Instructions

It is parametric. You can change the OpenScad file and adjust it to your hand.

List of things you will need:

3 x 608ZZ skate ball bearings
1 x M5 threaded rod 140 mm
6 x M5 small washers
6 x M5 nuts
4 x M3 hexagon bolts 19-20 mm
4 x M3 nuts

Print the hand grip part two times and the bearing adapter three times. If possible, try to prevent the thermal bending with a heat bed. Mount the bearings, M5 washers, nuts and adapter parts on the M5 rod the same way shown in the picture. The rod should be kept inside the hand grip by the top and bottom washers. Just put enough pressure on those washers, so that the rod doesn't shake. Use the M3 bolts and nuts to close the hand grip. If you want, use an anti slip grip sports tape on your print. Finally you can attach your favorite shaft coupling.

Update: Thumb mod
With this wheel you can rotate the rod with your thumb. Insert a M5 nut into the wheel's nut trap. Then fix it on the rod with a shaft coupling. You can cut a screw thread into the shaft coupling to make it more stable.

I bought the shaft coupling from Ebay. Search for "Kardan Metal 4mm".

Hand grip with bearings