Scientific Bulb Holder in Parallel - Made of hard plastic with four E10 sockets and two 4mm banana plug terminals. Can be used inline with other components of Eisco Series PH1029 Accepts size E10 Screw bulbs - Miniature Edison Screw (MES) of all different voltages This holder demonstrates the concept of a parallel circuit. Comes with 4 bulbs. Power Source needed for operation. An Economical Eisco power source is PH0971DCAC which is not included Base measures 5.875" (149 mm) x 2.875" ( 73 mm) x 1.375 ( 35 mm) Eisco offers a number of different voltages of replacement bulbs that will fit in this holder ( PH1014A 1.5 Volts Pack of 10, PH1014B 3.5 Volts Pack of 10, and PH1014D 6 Volts Pack of 10) Not included with this listing. Scientific Bulb Holder in Parallel - Made of hard plastic with four E10 sockets and two 4 mm banana plug terminals. Accepts size E10 Screw bulbs - Miniature Edison Screw (MES) of all different voltages. This holder shows the concept of a parallel circuit. Can be used inline with other components of Eisco Series PH1029 Comes with 4 bulbs, Base measures 5.875" (149 mm) x 2.875" ( 73 mm) x 1.375 ( 35 mm). Eisco offers a number of different voltages of replacement bulbs that will fit in this holder ( PH1014A 1.5 Volts Pack of 10, PH1014B 3.5 Volts Pack of 10, and PH1014D 6 Volts Pack of 10) Not included with this listing. Power Source needed for operation. An economical Eisco power source is PH0971DCAC which is not included