MH bulb question

[olgakurt]

This is from a garden discussion (growing peppers) and someone was asking me about the difference in size of these two bulbs. I think they ordered one which is a different size than what's in their pendant. Does anyone know how these two types are classified so they can gett the right one next time? I built my own MH system and ordered the bulb and bought the socket at an electrical store and wasn' t aware the bublbs came w/different base sizes.

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Mercedes Benz CLK GTR

 

[MattM]

The one on the left is a "medium base" with either an ED-23-1/2 or ED-28 shape.

The one on the right is a "mogul base" with an ED-37 shape.