Its is not a P60 drop in as its a bit bigger than that. You are right its more like a E1 style but bigger see pics. I know very little info on it and also found out more about this light recently on the FB group talk with PK.
I have no info on the bulb but this is it.
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Info on the bottom of the light.
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Check the size of the tailcap threads.
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from the catalog
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A drawings PK sent me years ago.
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To the member who I just refused to sell the M2D light too (in the PM's) I should explain more to you why. This is a very rare light really the only one in the world when you think about it. I would hate to see this light turned into a user after being so well looked after all these years (15 years in my hands alone) and end up being scratched or marked it really belongs in the hands of a collector.
I know I probably will have no control what the buyer ends up doing with this light but I hope it ends up in the hands of a collector and kept in mint condition.
Hope you are ok with my reasoning.
That's great. So far all the lights have been arriving around the world safe and on time.
That's super cool info, thanks for sharing. Any markings on the lamp assembly? Looks like there's some writing on its flange