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