The J3 is like many other 5.1.1 roms. Not many legitimate root methods available. Kingroot is no different. It however does offer a temp root method that must be reapplied after each reboot. What it is good for: 1.Debloating Rom. 2. Customizing Stock Rom. 3. Does Not Trip Knox. What it is not good for: Using anything that requires root upon boot of device like Xposed,Init.d,etc. For now it is the only real root method I have been able to find. It is a guess but I believe the devices kernel will need to be modified in order for proper root to be achieved. Installing stock firnware in case you run in to issues while debloating and modding your apps and system is the only fall back the device has but works fine. All you have to do is install odin and use it to flash the device 5.1.1 firmware to return to stock. This will reset the device to officical from custom in case you need to use your warranty or wish to sell the device. Install Kingroot,click to try root. It wont be successful but will offer root method at bottom of app. Press Try It. Now you have temp root. Do not reboot until you install any root ready file manager for debloating and also until you are done debloating. After reboot youll need to repeat the kingroot method again to make other changes. Firmware For Sprint Variants Android 5.1.1: https://samsung-firmware.org/model/SM-J320P/region/SPR/ Firmware For U.S. Celluar Android 6.0.1 : http://downloadmirror.co/android/2zSD/USC-J320R4TYU1APE1-20160518114917.zip (Not sure king root will work on the U.S. Cellular version as it is Android 6. But it may. Can give it a try.) This firmware is for Sprint device variants like Boost and Virgin Mobile. Also is main firmware for Sprint. Use Odin to install the firmware if it is needed. The firmware will revert the device to full unedited stock. For guides on how to use Odin and flashing the firmware in detail use google. Its your pal.