When buying temporary locks to braid into your hair for 1-2 months at a time, you can do slightly different installs. A single-ended dread (SE) has a loop on the end where you pull the hair through and braid it down. These tend to look nicer when installed around the hairline as they are more subtle looking.
Double-ended dreads (DEs) allow for a fuller install with fewer sections. They are basically one long dread which is folded in half and braided down one “leg” to install it.
So if you’re into temporary synthetic locks, that hopefully explains it. If you’re curious to read a fabulous comprehensive guide on the topic (with pictures, ooh!), check this one out:
Now, if you are looking to extend your real locks that are already on your head, you cannot buy SEs or DEs and expect them to work appropriately.
You will have to search instead for “permanent dreadlock extensions.” My friend Anouk Dreadmaker makes fabulous ones and can customize them to fulfill your wildest dreams. Her shop (and the section for permanent extensions) is found here: http://www.etsy.com/shop/AnoukDreadmaker?section_id=13273973&ref=shopsection_leftnav_2
I hope this helps you!
I am just popping in retroactively to say that Black Sunshine has also made a post about the topic that you may find helpful!