I have a block of code that i'm trying to covert from an old qt file into C# but i'm a little unclear what is going on in the struct within the union below. I'm not sure what the ':' does... i'm guessing it sets the size but could not find any documentation on this. Also since C# does not have unions what is the best practice for converting something like this. Thank you 

```
union uAWord
{
   uAWord()
     : m_AWord(0) {}

    struct sBcdAWord
    {
      quint32 m_O  :8;
      quint32 m_S  :2;
      quint32 m_D  :18;
      quint32 m_SS :3;
      quint32 m_P  :1;
    }
    sBcdAWord m_F;
    quint32 m_AWord;
}

```