Bridas are usually known as cable or zip ties. Here's a good picture of what your description refers to (the bridas are on the right)...you can see the horizontal lines all the way down (that's the "forma de sierra" your text mentions)

http://us.st11.yimg.com/us.st.yimg.com/I/yhst-24067115789173...

Nylon 6 inch Zip Tie and Nylon Anchor
http://www.coolerguys.com/840556021568.html

Click on the photo here and you'll see how they work: http://www.svc.com/ziptie-grn.html

A cable tie (coll. also "strap", "rat belt", "mouse belt", "tie wrap", or "zip tie") is a type of fastener, especially for binding several electronic cables or wires together, and to organize cables and wires.

In its most popular form, a cable tie consists of a sturdy tape of plastic (usually Nylon) with an integrated gear rack, and on one end with a ratchet within a small open case.

Once the tip on the other (usually pointed) end of the cable tie has been installed and pulled through the case and past the ratchet, it is prevented from being pulled back; the resulting loop may only be pulled tighter. In two of its most common uses, this allows several cables to be bound together into a cable tree, or to be used as makeshift handcuffs.

If a tied loop needs to be opened again, then, rather than having to destroy the cable tie by cutting the tape, it may be possible to release the ratchet from the rack (either by design, or perhaps using a needle and to reuse the cable tie.
http://en.wikipedia.org/wiki/Cable_ties

As you can see, the Wikipedia article calls it a plastic "tape" (your "banda") and the orificio is called an "open case". The "forma de sierra" is the "integrated gear rack".

Just so you can confirm, here are some very nice photos and drawings of "bridas" in Spanish:

http://www.cieffeplast.com/spagnolo/ProdottiFrameset.htm


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Note added at 9 hrs (2006-06-23 10:38:39 GMT)
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Maybe I should add that I'm well acquainted with "bridas" -- my husband is a computer guy and we always have them around the house.