Incra IMS2 24-Inch Incra Miter Slider
If you're planning on making a sliding jig or fixture for your woodworking shop, the INCRA Miter Slider is exactly what you need.  These inexpensive aluminum runners adjust for PERFECT sliding action in any standard (or near standard) 3/4-inch by 3/8-inch miter gauge slot with just a twist of the wrist.  Won't warp, shrink or swell like wooden runners.  Includes plans for a wide variety of shop-made jigs and fixtures.  Anodized aluminum for durability and beauty.  Available in 18-inch and 24-inch lengths.