Mueller Insulated Ultra Tech Test Prod with Stainless Steel Tip Insulated Ultra Tech test prods with stainless steel tip and nylon housing. These test prods are compatible with both insulated, non insulated or retractable 4mm banana plugs which are connected via a 4mm nickel plated brass banana jack. The length of these plug-on test prods is 159.3mm and they have a safety shock guard collar.