many thanks for all the replys guys , it sent me investigating even deeper - so i stripped the sliding head off to see if it looked pro' tradesman made , something i really enjoy doing - i seem to have ended up as the "what - is - it " guy ...in our NZ vintage tool club ..my background as a mechanic then later in engineering and fitting / welding certainly helps me understand tool production & modification methods etc, the interesting thing with this head is the perfect "zig-zag" machine cut near the pipe jaw and it is absolutely identicle and even on both sides ..it does appear to be factory done, I only found years of ordinary grease and grime in side the head - no fibres or unusual compounds and yet the top of the head is still very open and loose with a big enough gap to let in something objectionable - i think being modified was a good guess ..but it doesnt quiet add up - it would have taken half a day to a full day to achieve it when ordinary more enclosed spanners where commonly available at a low price , there are no Patent numbers to anser that question - but just 2 large number stamps on the main slide area just down from the top head - which incidentally are on all my other B&C combo's too - i thought they were production date stamps at first , all done by hand ..with the same unusual font ..and not alighned carefully - some have a letter too like a capitol "J" which i thought may be January, that one reads J 2 05 , another reads just A 29 , the unusual plated jaw one has simply 5 4 , all are stamped on the same side of the main slide (you'll see it when the pipe jaw is pointed to your left) and all are the same font , they all came from different areas -towns - villages etc ... 7 in total, as you say we can only speculate .. but if u guys can keep a watch out for anything similar ..it may help to solve it .... can u please pass this on to any big-time specialists in the ajustable spanner field in the US for me - they may have seen another similar ..cheers , I saw a mini finger tool set on a post here so iv attached photos of an English set i have .. its in a nice orig' tin , with names for all tools in the lid , incl's screwdrivers / nut wrenchs / 3 types of swivelling tweezers / and a pyrogrip acc' ...enjoy