Scale crane fittings.Found a shop I have never seen before;had what I was looking for,although they are a bit bigger than I wanted,I think they will work.Unfortunately,comes in a pack of three or five which makes for quite an expensive exercise!
See at: activescalemodels.co.uk

Thanks for that,perfect!Out of stock at the moment like so much at the moment,but I now know where to try.

Try this site this is one of many from this company