On Tue, 10 Jan 2017 16:39:23 -0800 (PST), wrote:

What is a tombstone called by regular people?

The lamp socket.

To the OP, I am migrating all of my old T12F40s to LED as they go bad.
So far so good but considering most of these are 20-26 year old cheap
"shop lights", they have a lot to live up to.