I guess this is the right newsgroup for this one. Its not quite Sieg v Myford but you can't get more uk.rec.models.engineering than meccano.....
My 7 yr old has one of the (French manufactured) meccano sets. Alas, he is having difficulty because the nuts and bolts keep coming undone - and its turning him off it.
I don't seem to remember having that much trouble 45 yrs ago when i used to be an avid fan. Its not just him - even when i tighten them, they will still work loose with ordinary handling.
The bolts are different from those I remember - these are allen headed black things (diameter outside thread 3.5mm - sorry haven't got a thread gauge). The nuts look similar to my youth - square not hexagonal but i remember them as marginally thicker. There are many more bolt length options than I ever used to have as well.
There are some nyloc nuts in the set and I have also locknutted the critical ones and tried the old varnish trick on the thread but none of these are a sensible solution. I did ask the chap with all the Army Meccano models at Brighton exhibition earlier this year but he didn't have the problem.
I guess the nuts or bolts are cheapo with too much clearance and I would be perfectly happy to buy him some good ones if it means he xxx we can get on with the big crane with motor - but what do I get and where from - and would normal hexagonal nuts be Ok for 7 yr old fingers?