Locking clamps are physical mechanisms meant to keep a missile or other projectile in place.

In 2371, while attempting to sabotage Tolian Soran's solar probe-launcher, Jean-Luc Picard engaged the locking clamps, preventing the probe from being fired into the Veridian sun. By the time Soran realized what Picard had done, the countdown to the launch had already completed and Soran was killed in the resultant explosion. (Star Trek Generations)