I've listed a very hefty M42 converter on eBay UK - seems to be solid metal and very strong, doesn't have a chip or a rim for stopping down automatic lenses. Should be good for heavier lenses. Starting price £1.99 plus postage, £1.55 in the UK, more overseas Ends Sunday Feb 18th 19:08 GMT https://www.ebay.co.uk/itm/134924908036