Some short screws were longer than other short screws, so that had me guessing a bit. I purchased the 5-6 size which is what I normally wear and my feet are just at the very edge. I tried alternate inputs and checked voltage at the power unit. They were so comfy I didnt even feel the lava rocks while walking + they have enough grip to prevent slipping or falling. They?re light and easy to take care of. It also gave me another table top to put my things on when I walk into my room. The couplings are VERY tight and hard to connect the fittings to the pipe especially the blast gates2. But the fabric pulled away from the heel portion, and I started to get little pieces of the foam and fabric all over my house! Of course, I was at work. ?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????28cm?????????????????28cm???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????28cm????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????