Never rely on open hooks for use on tiedowns. There have been multiple cases where these hooks bounced free when driving on a rough road or when the car hit a bump. When that happens there is the risk of a tiedown getting wrapped up in a tire and destroying the boat, breaking a windshield, flying around and dinging up your car, etc. Older style Thule tiedowns used carabiners, but it seems that to save money they went to these open hooks.
I’ve used a heavy duty bench vice to close these hooks into loops.
I then used a marine grade quick link and swivel snap hook. (the colored nylon straps are for flagging on the rear tiedown salvaged from various projects). Black nylon strap loop goes over the stern in front of the rudder. I could have used a carabiner instead of the quick link , but that could be taken off and lost or misplaced.
Be careful using non-marine grade carabiners or snap hooks, especially in salt water environments, as the spring can corrode and fail allowing the hook to come free.