Exhaust fitting parts - best supplier in UK?

[TriumphZ3]

Hi y'all - just started a quick layup of my 1998 1.9; lots of jobs to do including fixing seat movement, wonky door dropglass, CAT replacement, front struts, brake discs and pads, and tank straps. All hopefully straightforward but in initial stages whilst the exhaust is coming off I've listed potential spares for reassembly. The four (copper?) flanged nuts, well little or no flange, between CAT section and manifold are strange - two were 15mm, the other two were 9/16. There was a smear of copper on one but the others appear rusted so metal? In any case, four required in best quality. I suppose I'll need a gasket too.
Other end of the CAT section at silencer, there is one bolt with a spring (Hart bolt?) and one normal bolt, so I'll need one with the spring to match. Who is a good UK supplier for these? I also bought a set of rear exhaust hangers on eBay but hard as rock, no way of getting them to fit as there's no flexibility at all, so need good fit-and-forget parts from a reputable supplier.
Incidentally what's the round ball-like thingie attached to the middle section of exhaust that doesn't appear to be attached to anything else? Anti-resonator or the like?

 

[Ianmc]

Good luck with the cat replacement; I found only an OEM one would satisfy the MOT requirement for the M44.

 

[TriumphZ3]

Cat replacement on-going; worse case scenario is OEM BMW for £1400 +, current scenario is a mate's scrapyard where there is a shedfull of removed Cats, and one can possibly be welded in. Given the state of the removed one this has been done before. I'm assuming that huge welded patch on the top is not original, nor the lamentable welds on either pipe?
I'm still trying to find a good UK parts supplier, manifold to downpipe nuts are required (four plus one for the centre bracket) and OEM are £12 each. NO WAY am I paying £60 for five nuts, and I'll need the gasket too. I'm spoilt for Triumph parts, many good suppliers out there selling replacement aftermarket parts, but I still haven't found one for the Z3.

 

[Ianmc]

Doesn't look too original to me!

 

[TriumphZ3]

Just back from the mate's breaker's yard. It does appear this one has been 'worked on' before now; to what extent we don't know. As it passed emissions recently he may split it again and fix the horrendous internal rattle, so see if that works, but he also talked about removing part of the insides (done it many times before, he says) which will fix the issue and still pass emissions next MOT. I don't think I've anything to lose in that even if this one fails next August, I'll still need to replace it with something and in the current state I'll not get any of the BMW deposit back that they require on exchange, so if I can find good S/H, great, if not then I'm no worse off than at present.
I phoned the BMW Parts Department at another dealers and the guy there reckons the quoted price of £12 per nut (!!) is incorrect - not quite the phrase he used - and it's a lot less.

 

[t-tony]

The plate on the top will for removing the broken up catalyst from inside to stop it rattling/blocking the exhaust. The reason it's on the top is so a bentctester can deny any knowledge of cat being removed. Some thing on boy racer whistling turbo diesels.

Tony.