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Help finding replacement bolts for rear diffuser

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I recently got a new diffuser, I went to bolt it onto the car yesterday but found many of the bolts had seized and starting rounding off the heads.  Pretty much every bolt was rounding off so I stopped for fear of making things worse.

I tried some WD40 which didn’t help much so I’ve ordered some proper penatrating fluid to see if that will help get the bolts off.

Assuming I do eventually get the bolts off I’d like to replace the whole lot as they can’t be in good condition now. 

I had a look on Deroure but can’t find them.

Here are two pages related to the diffuser and undertray assembly but I can’t see the parts for the bolts?

There are lots of 4mm Allen bolts, a couple 5mm Allen bolts and a few 10mm hex bolts. 

Any one know where to get replacements from? 




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This happened to me with a couple of pan head bolts on mine.  You can get stainless replacements from Screwfix or similar, I can’t remember the size that came off but I had 20mm long M5 and M6 in my workshop and used those.

If you can’t remove the bolts that are in there, you have 2 options. The first is to use a dremel or angle grinder with a cutting disc to cut a slot across the head and use a large flathead screwdriver to undo them.. The second is to grind off the head and use a mole grips to remove the stud afterwards.

Hope this helps,


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13 hours ago, electro_boy said:

I was hoping to get the bolt sizes / specs so I can preorder a full set to have them ready and quicken up the turn around time.

IIRC, the rear diffuser and rear undertray all use the same bolt size. M8-1.25 x 20mm w/ small wrench head (10mm). I'd recommend zinc plated steel over stainless steel; less worries about galvanic corrosion. 

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So all the bolts were well and truly stuck in, they did not want to move at all.  I live in a flat and the car park has limited space and access to power for tools etc  ...  plus I just don't have the experience for this kinda work.

So I ended up taking to a local garage to had to drill the bolts out and even do a bit fabrication to fix some captive nuts that where no longer captive.  Took them most the day to get the job done.  So in some ways relieved it wasn't just me being a numpty but then also had to fork out for a few hours labour at a garage.

Any ways all screws/bolts/nuts for the diffuser have been replaced with stainless steel ones and a dab of copper grease on them.   So hopefully next time the diffuser has to come off it'll be a much more straight forward job.   I also replaced the the allen headed ones with Torx ones so should be able to take a bit more torque before they start rounding off.

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