E-39 vs EX-39. Why are light bulbs so confusing?

[I.B. Washincars]

I was looking for some bulbs on 1000bulbs. The bulb I think I may want is EX-39 base. Will that work in an E-39 socket?

 

[MEP001]

EX-39 has a longer center probe - the bulbs are rated for open fixtures, and it's a safety feature to help prevent someone sticking their finger in the socket and getting electrocuted. It might work, but the bulb won't screw in all the way and if you're not careful you could damage the bulb or the socket.