Miniature Bayonet Base (BAY9s) Single Contact Miniature Bayonet Base miniature light bulbs have a
single contact base with a diameter of 0.355" or 9.017 millimeters and a
length of 0.53" or 13.462 millimeters. Bayonet bases or caps are often abbreviated BA, with a number
after. The number refers to the diameter of the base e.g., BA9s is a
9 mm diameter bayonet base bulb. The lower-case letter s
specifies that the bulb has a single contact on the bottom of the base.
The BAY9s base has one contact on the bottom and two parallel lugs on
opposing sides of the base approximately 60 degrees apart.