My car-top rack does not have any stable tie down rings. I wanted to secure my canoe, lumber and any number of other things, but wrapping a rope around the rack cross bar didn't do the job. The rack cross bar is made from extruded anodized aluminum and I was able to fashion tie down points with some carriage bolts, washers and rings.
This simple solution gives me solid anchor points to tie to on my roof rack.
Step 1: Materials
4 - 3/8 by 1" carriage bolts
8 - 7/16 washers
4 - 5/16 washers
4 - 3/8 rings
Step 2: Fitting the Carriage Bolt in the Cross Bar
The remove the plastic covers that cover the ends of the roof rack cross bars.
Select a carriage bolt with a head that slides into the "T" notch on the roof rack extruded aluminum cross bar. The bolt head may need to be flattened to fit into the groove.
The bolt should just fit so that, when tightened on the washers, the bolt tightens against the cross bar.
Step 3: Fitting the Cover on the Cross Bat
Drill a hole in the cover that just fits the 7/16 washer.
Slide the carriage bolt onto the cross bar.
Slide the cover over the washers and bolt and move the cover into place.
Step 4: Roof Rack Tie Downs
Tighten down the ring so that is solidly fixed. Repeat the process on the four corners of the roof rack.