What is the four-jaw clamp for chemistry experiments?

What is the four-jaw clamp for chemistry experiments?
The laboratory iron stand is a common teaching equipment in the teaching process of chemistry experiments in colleges and universities, and the four-jaw clamp is an indispensable part of the laboratory iron stand, which mainly plays the role of fixing the test tube clamp and titration clamp on the iron stand. . Its safe, convenient and quick use is of great significance for assembling a complete set of experimental equipment.