FixedSplit

public static string FixedSplit(string s, int len, string delim)
	{
		StringBuilder sb = new StringBuilder(s.Length + (int)(s.Length / len) + 1);
		int start = 0;
		for (start = 0; start < s.Length - len; start += len)
		{
			sb.Append(s.Substring(start, len));
			sb.Append(delim);
		}
		sb.Append(s.Substring(start));
		return sb.ToString();
	}