{HEAD ~ Extension sets} in accordance with the present invention may be sold as accessories suitable for {TAIL ~ use} with existing box section spirit levels and I beam spirit levels 
{ HEAD ~ Extension sets } in accordance with the present invention may be sold as accessories suitable for { TAIL ~ use } with existing box section spirit levels and I beam spirit levels
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH