You would always have a threaded rod sticking out of all sides , plus you would still have to center it in your sled. With the handscrews added to your sled, you could take a scrap 1x4 , drill a hole in the bottom for the handscrew dowel, and if you cut out a V-notch in each side of the 1x4's you could clamp square or even round pieces of wood in your sled. The right and left handed thread on each handscrew makes it really easy to center your wood block. You would only need one threaded rod down the middle of your sled, then attach a 1x4 to each dowel coming off the threaded rod.