We’ve covered miter sliders before, but here’s a different take on the problem from Micro Jig. Rather than use set screws or “adjusting disks” to fit into a miter slot without slop, their ZeroPlay guide bar uses two stacked half-bars that expand and contract along the entire length of the bar so it’ll work in any 3/4″ wide by 3/8″ deep miter slot — even Shopsmith and General miter slots.
Micro Jig manufactures the 9-1/2″ guide bar from a composite material. Two pins on the top bar ride two wedges on the bottom bar, so depending on which direction the bars move past each other, the width of the stacked bars either expands or contracts. When the bars match the exact width of the slot you secure them together with three button-head screws.
MicroJig claims the Zero Play jig is available at many online shops like Rockler and Woodcraft, but the only place we could find it was Hartville Tool, where you can get two ZeroPlay guide bars, two stops, some hardware, instructions, and jig plans for $22.