Thanks for that - it is a V clamp - but it's a really tight fit to get it out, so it's going to need some disassembly to get it off and replace - so I was hoping to be able to get sizing/spec etc from the Yanmar part no, and then find one (a better one!!) elsewhere and change it over, rather than disassembling twice!!
I'm a more than a bit unimpressed that it's broken, looks like a fairly crap mild steel tensioning bolt which has given up. It looks to be about the same quality as the paint job on the engine!!