PAR 46 Red Warning Bulbs & Headlights

The bulb size is a PAR 46... The two terminal bulb came in both a stab on terminal and a screw terminal and both have different part numbers. The 4000 bulb is a 3 pronged bulb and generally listed for motorcycles. I don't know why they have a different part number, but it might have something to do with shock resistance.
So the line up of PAR 46 bulbs are.......
4000 = motorcycle 3 prong headlamp
4001 = clear low beam automobile
4002 = clear high beam automobile
4001R = red bulb with 2 stab on terminals (warning light)
4002R = red bulb with 3 stab on terminals (warning light)
4013R = red bulb with 2 screw terminals (warning light)
4412 = clear fog light bulb used in the Federal SolaRay light

The back side of headlamp bulbs have 3 locating tabs on them, that must match up to the bulb holder. This was done to make sure that the high and low beam lights do not wind up in the wrong location on the car. Therefore, they are not interchangeable. Each must go in its proper location.

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Bulb sizes are designated by PAR numbers.

PAR-20 (2 1/2”)
PAR-30 (3 3/4”)
PAR-36 (41/2”)
PAR-38 (4 ¾”)
PAR-46 (5 ¾”)
PAR-56 (7”)
PAR-64 (8”)

notice the tabs on the back. they fit the slots on the cup. I don't know have many times I have walked past a car with the lights in crooked. because some one has either put the wrong cup in that position or they just don't have the sealed beam in the slots.