These valves are not standard for the Microlab 500. They do not have a luer leg where the syringe attaches. Instead they have a 1/4-28 threaded port. This type of valve is compatible with the ChemSeal style syringes that also have a 1/4-28 threaded port. If you are considering using one of these valves it is recommended that you contact a Hamilton representative to confirm compatibility with the application.