Ok this is pretty simple so don't make a big deal about it. The bore needs to be drilled out to 1/4" or .250". The outside diameter of the bushing is cut to .252" so when it is pressed in there should be a slight "pinch" and the inside diameter may shrink (will) so, to get the shaft to spin freely, you may need to run a bit through the bushing to open it up to a clearance fit. A 7/32" bit will work just fine. If the hole you drilled in the carburetor does not provide a press fit, do not worry. Just slip it in and once the throttle assembly is installed, it has nowhere to go. You can use any method to drill that you like but a drill press with a vise that allows you to match drill the upper and lower bosses will provide much, much better results. If the alignment of the two holes do not line up, binding will occur when rotating the throttle shaft. In this case you will need to open the bushings up until the shaft rotates freely. You do not have to bush the lower boss if it doesn't need it. These bushings will repair an out of round and/or oversize condition in the carburetor. If your throttle shaft is worn also, don't expect these bushings to take up all of the slop.