The word, grasp, means to seize hold of something with the fingers and hands. It often is used with a sense of urgency. For example, "he grasped tightly to the life jacket. He knew it meant his life to hold on". The word grip is very similar. It means to hold tightly, but more with determination than urgency. For example, "when I shook his hand, I felt his strong and steady grip in my hand". The word, clench, suggests strongly closing down on something. It suggests a close, tight fit For example, people clench their teeth together. The word, clasp, is different. It is associated more with an embrace of the arms as if to prevent escape. For example, "the little girl clasped the doll to her chest as if it were her only friend left in the world". Hope this helps

To me, grip, clasp and grasp are basically the same although a clasp can be a mechanical device used to fasten. While clench means about the same as the others, when I hear clench, I think of teeth clenching.