Nal are heavy stone dumbbells unique to India. They are circular in shape with a hole in the center. Passing through this hole is a cross piece which functions as a handle.
They can come come in progressive weights so as one may always progress onto the next weight. Not all Akhara are so equipped, though there will usually be a couple of Nal strewn about the training area.
Nals come in differing weights from very light (around 20kg) into extremely heavy (150 kg and upwards) . Lifts with lighter weights are done for high volume whereas the heavy weights are lifted for a few repetitions showing an inverse training paradigm. The Nal cans strengthen the whole body especially the pressing muscles including shoulders and triceps. The thick handles will really work your grip especially as you have to overlap your hands when using heavy nal.
The Nal has fallen in favour of the western style dumbbell and barbell. Favourite exercises are a clean and press, a hold of the weight overhead and holding the Nal behind the head to squat with. One Guru told me of Pahalwan who would use a 300lb Nal to squat with!