[mylesdw]

Maybe we are talking at cross purposes; on mine the bulb passes through the adapter and stops when the collar on the bulb hits the top of the adapter. The collar does not go inside the adapter but sits on top. It is not completely clear from the picture but if one end of the adapter is a tapered thread, it is definitely NOT the end that the nut goes on. I have not found a way of compressing my adapter drawing and still have it visible yet! Can you take a .DFT (draft) file of the drawing? Basically you buy a -12AN to 1/2" NPT straight adapter SUM-220246 from Summit and have the -12AN end machined to 3/8" BSP and a square end (no flare).