That is what is known as a BA15 base.
It is an 1141 or 1156 lamp (1156 is too hot for the fixture however). I use M4Products LED lamps as they are the best I have found. For Interior lamps I prefer natural white, and have
this lamp installed in all of my ceiling fixtures.
When I bought my trailer it has a hodge-podge of LED lamps in different color shades and many of them had non-working LED elements. I install all of the same M4 Elite natura white lamps and save the very few that were sorta good and put them in the exterior lights over the dump station, the cargo pod and the exterior storage compartment lights.
The nice thing about M4Products is that they design the circuity and specify the Samsung LEDs to be used, no matter which style lamp it is. I installed all Natural white and the reading lights, the puck lights, the ceiling lights, all are the same color.
I've converted 3 different RVs and so far only one bi-pin lamp in a puck light has failed, and M4 promptly replaced it. I have never had an LED element fail and I leave them on a lot while I am working inside setting up for a trip or doing repairs.
Charles