English to Spanish Tech/Engineering Mechanics / Mech Engineering

I cannot find the right term in Spanish for u-nut. I know that the literal translation "tuerca en U" o "tuerca en forma de U" is not correct. Take a look a google images to see the part (it is a kind of clip with a nut in its upper part)

http://images.google.es/imgres?imgurl=http://oemfasteningsys...

http://images.google.es/imgres?imgurl=http://www.keeptheheat...