Slip floats do as the name implies. They slip on the line to a predetermined stopping point, allowing you to fish any depth you desire. Most floats can be used as slip floats. Any float with a central hollow core from top to bottom will serve. To rig the slip float, you need only two additional items – a bead a stopper .
To rig your slip float first attach a stopper to your mainline. Next thread your mainline through a small bead. Then thread your mainline through the hollow tube of your float and attach a swivel in the usual manner.
For a stopper most anglers use a nail knot tied with brightly colored dacron line. Several manufacturers market nail knot stoppers. These hollow tubes upon which one to six nail knots are tied. To use these you slip your main line through the tube then slip a nail knot from the tube onto your mainline. Now snug the nail knot very tight to your mainline and trim the loose ends. This knot will slip easily on a wetted line and is very visible.
To fish a slip float all you need do is estimate the depth of the water you wish to fish and slip the stop an appropriate distance up your main line. Reel until you have a foot or so of line from the float to your rod tip and make your cast.
Once the float lands, the mainline will slip through the float and bead until the bead makes contact with the stopper. As you retrieve line, the float stop will pass easily through the rod guides. Likewise the stop should present no problem in casting. (If you leave about an inch of line extending from each end of the nail knot it will slide through the guides more easily than if it is trimmed short.)