I want to use my Tri-Angle knife sharpener to sharpen a couple sets of handheld gardening pruners. You know the kind with a curved claw piece and a single pivoting blade that is used for trimming rose bushes and other vines and plants? Pruning shears, essentially.
Here is a link to an image of a similar type of shear.
It'll sharpen pruners just fine. Just be careful to not over grind the flat side (which you can lay flat against the flat of the stone instead of holding straight up and down).
I use the triangular rods freehand, matching the factory bevel angle. As already mentioned by thombrogan, don't do much on the flat side. Bypass pruners are a chisel grind. You want to "back off" the flat side to remove any burr.