This rod clamp allows you to connect two 8mm rods at any angle you want. The scad can easily be modified for other rod sizes. Intended for a diagonal reprap support.
Print 2, clamp around rods at desired angle and secure with an M3x25 screw (with nut and washers). For a diagonal brace like the one in the picture you'll need an 8mm threaded rod around 25cm long. For extra strength and vibration control, you can put something soft/rubbery between the two halves, but then you'll probably need a longer screw.
The scad file is parametric, so you can make it stronger or fit other rod sizes.