Midget Grooved Base (S5.7s) Bulbs have a single contact on the bottom
and a base diameter of 5.7millimeters. The diameter of the groove
between the base and sides of the base is 4.8 millimeters. Midget
Grooved Base (S5.7s) Bulbs are either TL-1 1/2 or T-1 3/4 shape by
design. The Midget Grooved Base (S5.72s) is sometimes referred to as
(S5.7s9) or (S4S/8).