Here's some sizing info: (courtesy of NiMo)
VSW006 has 52mm shaft (VSW006-01) connected to a 0mm offset wheel shaft (VZW054-02).
VSW007 has 50mm shaft (VSW007-01) connected to a 2mm offset wheel shaft (VZW055-02).
also:
VSW015 has 50mm shaft (VSW007-01) connected to a 0mm offset wheel shaft (VZW054-02)
VZW054 has a 45mm shaft (VZW054-01 connected to a 0mm offset wheel shaft (VZW054-02)
VZW055 has a 40.5mm shaft (VZW055-01) connected to a 2mm offset wheel shaft (VZW055-02)
VZW058 has a 40.5mm shaft (VZW055-01) connected to a 0mm offset wheel shaft (VZW054-02)