The Sontaran fragmentation grenade was one of the most dangerous weapons used by the Sontaran. It was a small, egg-shaped sphere with an indentation on the top. It would completely annihilate everything in a small blast radius once it was activated.
The Master obtained a fragmentation grenade and used it to try to kill the Third Doctor. He commanded Professor George Philips to throw it at the Doctor, but the Doctor and Jo Grant were able to convince him to stop at the last second. He threw it away from the Doctor, but Phillip was killed by the blast. (PROSE: Doctor Who and the Terror of the Autons)
Nic Reece was also able to obtain two fragmentation grenades. One he used to booby-trap his room on Peladon. The other he kept on his person and intended to use it if he was in danger, though Bernice Summerfield threw it off a cliff when he tried to use it on the Seventh Doctor. (PROSE: Legacy)