Originals of these are not that common. They were a consumable item and sets usually have replacements. The original included bulb or lamp is a large spherical bulb. Not flat topped, not small, not modern! They are 26.7mm (1.05") overall and the bulb glass is 14.8-15mm (0.586") wide. The edison screw portion is known in nickel and brass but most originals are nickel plated. They are 3 1/2 volts and this is marked at the base of the bulb.