Approx 2.5cm. Pretty much the same with as the 'cleat' type tie down straps, although the nylon they're wowen from is thicker and more durable.

If the rack would clear the body work, hatch huggers allow the rack to be fitted where the metal hooks may not (I used two sets - x4 straps on my VW Passat 2013 model). In theory use could replace all the straps with hatch huggers (although seriously consider how many bikes I hung from the rack if rpalcing the top metal fixings with hatch huggers).

Not sure this anwser will be of use, but I used two sets of hatch huggers (that's x4 straps) on my VW Passatt 203 model. I'd be happy if need be to go to three sets if my car required them (although I'd be mindful of how many bikes I hung on the rack if replacing the top fixings with hatch huggers, although I can't see why the plastic 't-bar' would be any less robust than the orignal metal hooks.

PS - I've replaced my the side and bottom metal fixings with hatch huggers.

hatch huggers are great, but they aren't secured inside the boot. If using them as top fixing the rack would almost certinally want to fall off (espacially if bike were still loaded!).

Less of an issue is used for side / bottom fixings, although before opening boot you'd want to loosen the straps, and once re-closed you'd need to re-tighted them.

Although a bit of a pain I found theat once a tailgate rack is fitted is isn't always easy / possible to open tailgate without the 'hooks' damaging / catcing on paintwork, so hatch huggers are in most circumstances no worse than the original 'hooks'.