2001 Ford Expedition Sway bar bolts continually come off

Hello, On my 2001 Ford Expedition the front sway bar link bolts have begun continually coming off. I have replace them 4 times. I always know when they have come off because of the noise as the bolt goes under the car.

I drive very bumpy and curvy roads to and from work for a total of about 19 miles per day. I live in England where the roads are not that great anyway.

There are no shops which will work on the car here because of it's originality here and therefore I have to do everything myself. I do have access to a shop with a lift and tools on the US Base here. I have been replacing the bolts which ordered from the US and are listed as replacement parts. Do I need heavy duty? I really like my car and want to keep it going for years to come.

I also tried to pay ( donate question) but somewhere in the process it locked up on me.

Can you help with the sway bar link bolt issue, please?

Adam