These blunt needles are designed with a standard Luer-Lok hub for use with widely available Luer-Lok syringes.  The needles are available in a variety of diameters (gauges) to accommodate different sized openings.  As a general rule, it is best to use the largest diameter or gauge (smallest numerical gauge value) that will fit the available opening in the electrode since viscous gels may require considerable force on the syringe plunger to force the gel through a small needle diameter.  The Luer-Lok syringe tips are available in different diameters (gauges).  Be aware that the tip opening in the 16 gauge Luer-Lok blunt needle may require significant plunger pressure (accordingly – hand strength) to dispense viscous gels and pastes.  We generally find that SignaGel and Lectron III Chloride 10 gel are the best choices for use with LuerLok syringes and all work fine with 16 gauge or larger blunt needles.