Luer Lock Syringe tip caps twists on the end of any Luer Lock syringe,
press fits on a Luer slip syringe or twists into luer lock bottle caps. 
Different colors is available.

Luer Lock Syringe tip caps connect to all syringe tips in place of a dispensing tip,
and come in several different colors.
These caps are designed to keep material inside the syringe or bottle from curing and drying.