Posted 14 April 2017 - 01:58 PM
The majority of bolts on a Mini should be UNF with some UNC. However later models sometimes used Metric Fine in a few places where there was a nut rather than a tapped hole。That was not a good move as MF is weaker than UNF due to the deeper thread root and provides less clamping load due to the larger thread pitch. As you need UNF in most cases, best stick to it everywhere. Then there are only AF spanners involved and no confusion and chewed bolts heads.
Almost all the bolts were Grade S which is the old B.S. grade equivalent to the ISO 8.8 for Metric bolts. The US grade 5 is equivalent. On no account use Metric grade 5 which is the stuff you might buy in B&Q, and is dangerously weak for automotive use. Make sure you get matching nuts, property class 8 or S, and please, only from a reputable supplier which openly states the grade of their products on their web site. Lives depend on some of these bolts.
As already said, stainless must not be used on any functional part. Grade A2 is dangerously weak and A4 is too brittle. You can use it on unstressedtrim etc and things like the self-tappers holding the rear window mechanism are sometimes stainless.
The companies selling sets of bolts are mainly selling Chinese junk and should be avoided at all costs. Counterfeiting of high tensile bolts is widespread. Those selling stainless frankly should be avoided for all your automotive needs, because if they have something basic like bolts wrong, what does it suggest about everything else that they sell? There are lots of spivs and fraudsters in the business. Caveat emptor.
