So I am guessing the first question is.. What is Travel Sentry? It's a good question, they are a company who devised a standard for luggage locks so they can be opened by a Master Key by Airport Security - most notably the TSA (Transport Security Administration) in America. This means that instead of having to take some bolt cutters to your lock to make sure you're not smuggling in radioactive material or gun powder they can use their magic master key to open the lock, do the security check and then lock your suitcase back up and send it on it's way. The combination lock prevents having to play "where did I put the key for this?" before travelling and the twin pack "Yours & Theirs" should prevent any fights from breaking out over whose luggage needs locking up the most! Dimensions (W/H/D) - 3 x 5.5 x 1.5 cm (incl. shackle)Material - 46.2% Metal Zinc Alloy 27.7% ABS 26.1% Metal Steel