Selby's Spiral Shelf Support is a great solution for shelves that become unstable over time due to slight warping, wear and tear, or poor installation.
During or long after installation, a simple turn of a screwdriver can adjust the support 2mm up or down. Pins are 7mm long and are available in 1/4" or 5mm diameter. Standard color is clear. Available in light brown, dark brown, gray and black on special order.