What bulb does this use?

I bought a glass display case off of someone on Facebook Marketplace and it has a light fixture to light up the case. It came with no bulb and she said she hadn't used the light in years… The case says it was made in Denmark. I can't figure out what kind of bulb fits in the fixture, an E26 does not fit. The outer diameter of the socket is 25mm and the inner diameter of the socket is 24mm. If anyone has any idea what bulb it takes please let me know. Thanks in advance!