Today, I investigated.





These are (apparently) T-1 form factor incandescent lamps with wire leads. That lamp is 3mm (~.118") diameter -- that's less than 1/8" !
In this close-up, you can make out the broken filament, on the lower leg:

After carrying it around in my pocket for a while, the filament got worse:

Newark sells a pack of (10) of these for $8, Their stock No. 50N8118, SPC TECHNOLOGY number 2182


I imagine that getting the lamp back into the soft silicone holder, and wrapping the leads correctly is going to be quite difficult for my fat fingers. These things are small:


