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Chasing threads
Hey guys, I just bought a Thule roof rack for my Renault Grand Scenic.  The rack uses fixed mounting points (bolt on).  I went to mount it this weekend, and found that the mounting points were a bit rusty, one especially so.  The car is secondhand, and there are usually plastic bolts in the fixing points, presumably to prevent corrosion.  These bolts are absent on my car.  I am unable to thread the bolt in more than a few turns in the especially bad one due to the rust.  The threads on the bolt were even flattened by it.  These bolts are being replaced by Thule free of charge.

I assume the best way fix this would be to chase the threads in the internally threaded fixing point?  Is there a better way, such as using a solvent?  The fixing points themselves I think are replaceable, but on other car makes (all I could find), you have to remove the roof liner inside the car to get at the bottom half of the mount, so I've ruled that out.

I've determined with 95% certainty that the bolt size is M6x1.0, 15mm threaded section.  The Thule UK distributor didn't know the size, and didn't seem to want to help other than by sending new bolts out.  What is the best tool to use to repair the threads?  I know the difference between "chasing" and "tapping", but could a tap be used?  Cheers.
If I understood your scenario correctly you have an internal thread that’s rusty and need it clearing out. If so you need to go a tool shop and buy a tap. If you take the bolt with you the shop they will size. Alternatively someone on here may have a selection of taps. If it is an external thread you need a device called a die. Looks like a large nut but very hard. I hope that made sense.
Just a thought but how about trying to scrape all the rust out with a small wire brush?
Where is Tinc when you need him!?
Maplin do a fairly reasonable tap and die set for cheapish.
2010 Canyon Aeroad 9.0 SL
2014 Specialized Epic Marathon
Thanks for the replies.  I ended up ordering a tap and die set off Ebay for less than a tenner.  I figured that if the corrosion was strong enough to flatten the threads on my bolt, a wire brush or solvent were unlikely to clean the mounts fully.

I've read it's best to lube the tap before and regularly during use.  I don't have anything other the wet or dry chain lube hanging around.  Will either of those be sufficient for this small job?
Get yourself some 3 in 1 oil also useful for other jobs around the house. Don't forget when using the tap one full turn in half turn back and so on until you reach the end of the thread. If you are tapping a blind thread best to take the tap back out at the half way point to clear the swarf out of the hole. Also use a finish tap
Or just cut a slot in the side of a correct sized bolt and with WD40 or 3in1 just ease it in and out until the thread clears.

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