Any Ideas On These Bolts?

Still available to buy new
https://www.fowlersparts.co.uk/parts/6789/sprint-st-from-vin-208167-/rear-sub-frame-fittings

 

A couple of bolts like that can be had cheaply from your local fastener suppliers, in stainless steel, for less.

 

If you replace rusty parts with like for like then they will also rust eventually, not to mention the cost of original fasteners.

Buy yourself a cheap thread gauge which you can use to check the thread pitch of any fasteners then buy stainless replacements. A2 stainless is corrosion resistant whilst the more expensive A4 is only required for highly loaded applications.

I mostly use Westfield (https://www.westfieldfasteners.co.uk/) and Namrick (https://www.namrick.co.uk/) but others are out there. Its also worth buying a mixed pack of stainless (M6, M8 etc) to replace old fasteners as you come across them.

 

A4 is often referred to as marine grade for its enhanced corrosion resistance but you can also get A2-80 and A4-80 which are high tensile versions. Even higher tensile strengths are available if required, but at a cost. My favourite supplier is Accu who supply some F1 teams.