Screw caps are the most common type of cap for GL45 reagent bottles. They feature a threaded design that allows for a secure closure by twisting the cap onto the bottle neck. Screw caps provide a tight seal, preventing leaks, evaporation, and contamination of the reagent. They are often made of materials such as polypropylene or high-density polyethylene (HDPE), which offer good chemical resistance. Screw caps can be easily removed and replaced, making them convenient for frequent access to the reagent.