buy it
Ok this is what you would use on a shimano hub to give it a standard freewheel threading.
but why? shimano hubs are trash anyway, once you put a decent freewheel, say a tensile 60 click ( £35 ish ) thats getting up to £95.
Or buy a because screw on hub and use a tensile freewheel ( either by welding the lockring / supergluing it shut or buying a RFW version ) which would work out approximately the same price, ( in reality £10 cheaper ) leaving you to spend £5 extra on the new spokes necessary.
because hub
You would then have a very strong wide flange wheel build, sealed cartridge bearings and a far more specific wheel instead of a heavy kludged solution. This would also be massively lighter too, and transfer the weight to the front of the bike if you used a front freewheel.