2 Frosted Push-In Style Bulbs.  9/32 Base.  15 Watt.  Works in most vintage and older model sewing machines.

Will fit the following models and many more:

Bernina:  707, 717, 740, 801, 830, 840, 900, 910, 930, 940
Singer:  400, 500, 600, 700, 800, 900, 2000 (Most old models)

Part # 15T7F