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The air will leak out. You need that sand to prevent the pipe from collapsing. I used table salt to fill a 1/8" piece of copper tubing I cold wound into a coil. No 'ovaling' at all!
You can make leather lace the same way. Start off with a disk shape, cut into it like with the bottle, and pull through steadily. Leather stretches, so an even pull is necessary for an even lace.
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OK. Well yes, the freewheel is in the hub, not the wheel. You can screw on a freewheel that has a single cog, like on a bmx, and now you have a singlespeed (the chainline between the chainwheel and cog will be way off). Or you can screw a single cog onto the wheel threads, even with a second nut, and it will unscrew and fall off the first time you put back pressure on the pedals, and you will not have a fixie. To make a fixed gear setup, one needs to lace the wheel to a (track) hub which has no freewheeling ratchet mechanism and has opposing lockring threads, or buy a wheel that has a fixed (track) hub that has opposing lockring threads laced onto it, or 'fix' your existing freewheeling hub as per my video.
Fixie Hub ConversionView Instructable »
BushLightView Instructable »