Here is an example of Interlocking maintenance done on 7 Month young permanent loc extensions. 

FAQ: "So, What's the difference between coil twist & interlock maintenance on loc roots and I heard that it is bad for my locs"? Interlocking method gets a bad rep amongst some loc wearers but it's not the method itself that's damaging; its the incorrect way some people do the method and doing it too frequently or tightly that causes damage. Incorrect interlocking includes pulling the loc through the same space more than once and producing a gap at the scalp that resembles a Y shape. As the new growth pushes the loc away from the root, this Y shape does not close. A repair will be needed to restore the loc to good health otherwise thinning or damage can occur. Please be sure a professional is doing this method for you, or you have necessary skill to prevent damage. Also ensure there's enough new growth in between interlocking. I usually recommend once every 2-3 months depending on the texture of hair and condition of my client's scalp. Coil twisting the new growth (by means of palm rolling or finger twisting) tames the roots for only a short timeframe, while interlocking intertwines the new growth down  to the scalp. This method is desired by clients  seeking a longer lasting maintenance. Benefits of Interlocking: 1. makes the root stay tight and neat longer. 2. It's recommended for anyone with resistant soft hair that won't lock, or for anyone who has many inches of new growth 3. Anyone who is very active and sweats a lot. 4. Any one who experiences their hair unraveling in a short time after getting palm roll method. 5.Anyone who wants to save money and not have to go so frequently for retwist.