What kind of bulb?

Hey guys, the oven light on my Frigidaire oven went out as I have to leave it on a lot to keep my sourdough starter warm. Well I took it out and to see what kind it was so I can replace it but there’s no info on what size I need to get. The only writing it has on it is “120v 40w” but now I need size. Any idea on how I figure this info out? Thanks!