Important to install or remove thule lock cylinders you will need a change key.
How to install thule roof rack locks.
Enter the part number below to search for keys and locks.
Then try using the locking key.
Thule lock cylinder installation instructions presented by rack outfitters.
Press your finger against the lock cylinder to keep it in place and use your other hand to pull out the master key.
If you have lost the change key enter d1251 in the search box below to order a replacement.
Cargo lock rstallaticn or 180.
Enter the exact code found on your lock cylinder otherwise your lock might not be found.
You would need to insert the change key into the lock core insert the core into the thule accessory and then once you remove the change key the core will be attached to the thule accessory and be ready to be locked unlocked.
What you need is the change key part 853 1251 to install new lock cores like the part thlockn168 that you referenced.
Remove the master key and try the locking key.